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May 17
Watermelon Disease Update

Most watermelon growers are in the process of placing transplants in the field.  I have received several commercial samples of transplants still in trays prior to out-planting.  The two diseases I have observed so far are gummy stem blight and bacterial fruit blotch.  Below, I discuss these two diseases as well as management options. 

Gummy stem blight on transplant seedlings may be recognized by the watersoaked area of the stem (botanical term:  hypocotyl) as shown in Figure 1.  The watersoaked area may eventually turn brown and woody.  A closer look at the woody area may reveal the small, dark fungal structures of the gummy stem blight fungus (Figure 2).  The true leaves of watermelon transplants may also be affected. 

The fungus that causes gummy stem blight (Didymella bryoniae) may survive in crop debris, thus overwintering in the field from year to year.  This fungus may also survive in seed.  It is also possible for the fungus to survive for short periods in greenhouse production facilities. 

Crop rotations with non-cucurbit crops for 3 years will help to lessen disease severity.  Preventive fungicide applications may be scheduled with MELCAST, a weather-based disease forecasting system.  Contact fungicides such as chlorothalonil (e.g., Bravo, Echo, Equus, Initiate) or mancozeb (e.g., Dithane, Manzate, Penncozeb) should be alternated with systemic products such as Luna Experience, Switch, Inspire Super or tebuconazole (e.g., Monsoon).  Not all of these fungicides are labeled for other fungal diseases such as anthracnose.  Remember to alternate modes of action by using the FRAC codes of the fungicides.  See the Midwest Vegetable Production Guide for more information. 

The symptoms of bacterial fruit blotch (BFB) can be difficult to recognize on foliage.   Leaf lesions may be angular and appear to run along the vein (Figure 3).  The lesions may appear watersoaked, especially when viewed on the underside of the leaf.  Leaf symptoms of BFB are easily confused with angular leaf spot, a disease that is not often economically important.  A laboratory analysis may be required to distinguish these two diseases.  The relatively large, oily lesions on fruit are easier to recognize (Figure 4).

In contrast with gummy stem blight described above, the bacteria that causes bacterial fruit blotch (Acidovorax avenae subsp. citrulli) does not readily survive in crop residue.  The bacterium is known to survive in seed.   It is possible that the bacterium may survive in greenhouse production facilities for short periods. 

Once BFB is detected in the field, applications of a copper product tank mixed with a  mancozeb product may help to lessen disease severity.  Whether BFB is detected in a watermelon field or not, updated recommendations are to apply copper 2 weeks before first female bloom, at first female bloom and 2 weeks after first female bloom. Additionally, application of the product Actigard at 2 of the 3 copper application times listed above is recommended. More information about these new recommendations may be found here​ or in the Midwest Vegetable Production Guide. 

Be sure to inspect seedlings for signs or symptoms of disease.  Avoid planting transplants that may be diseased.  

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Figure 1:  This watermelon transplant has a water soaked area just under the seed leaves, a typical symptoms of gummy stem blight.

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Figure 2:  A more advanced symptom of gummy stem blight is the light brown woody appearing area of the stem near the seed leaves.  The dark structures of the fungus that causes gummy stem blight may be observed with a 10X hand lens. 

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Figure 3:  Lesions of bacterial fruit blotch of watermelon on transplants may include angular lesions that may appear water soaked. ​

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Figure 4:  Mature watermelon fruit may have large, dark, irregular lesions due to bacterial fruit blotch. ​ 

April 29
Fusarium crown and root rot of tomato

Symptoms of this disease include tomato plants with lower leaves that become yellow (chlorotic) and die; plants that begin to wilt; a lesion on the lower stem at ground level (Figure 1 and 2).  If tomato plants are removed from the soil and carefully split open from the ground level, a discoloration of the vascular tissue can be observed (Figure 3).  It is important to note that this discoloration does not extend up the stem more than 6 to 8 inches.  If the discoloration extends up into the plant canopy, the disease maybe Fusarium wilt of tomato.  Although growers may observe multiple plants begin to die of this disease over a period of days or even weeks, the fungus does not splash from plant to plant.  Therefore, there should be no plant-to-plant spread in the high tunnel.

Temperatures from 68 to 72 degrees F favor Fusarium crown rot and may explain why I observed this disease last week when the weather was relatively cool.   I often observe Fusarium crown rot in high tunnel or greenhouse situations where the tomato plants are grown in the ground.  This is because the causal fungus, Fusarium oxysporum f.sp. radicis-lycopersici, survives very well in the soil in the absence of the host. 

Crop rotations that do not include tomatoes or other solanaceous crops will help to lower the amount of fungal spores in the soil. However, since the causal fungus survives for years without a host, crop rotation is not a complete solution.  I also realize that many growers who produce tomatoes in high tunnels do not feel it is economically practical to rotate to another crop.  To such growers, I would point to this article about how to minimize diseases in high tunnels. 

Growers who plant tomatoes in bags or pots in a high tunnel instead of in the soil should avoid Fusarium crown rot since the fungus survives in the soil. 

Check with your seed representative or seed catalog for tomato varieties with resistance to Fusarium crown rot.  Most tomato varieties with resistance to Fusarium crown rot are indeterminate.  (In contrast, there are many varieties with host resistance to Fusarium wilt.)  It is possible to graft your favorite tomato variety as a scion onto a rootstock variety with resistance.  This table will help one select tomato rootstocks with resistance to Fusarium crown rot and other diseases.  Some tomato seed companies will sell grafted tomatoes. 

There are no fungicides to control Fusarium crown rot.  Most fungicides are for foliar use; I know of no fungicides that may be sprayed on the top of the soil.  Read the label carefully and contact me if you have questions. 

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Figure1:  The tomato plants shown here are stunted, wilted and the lower leafs are dying due to Fusarium crown and root rot.  

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Figure 2:  The lesion at the base of the stem is typical of Fusarium crown and root rot of tomato.  

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Figure 3:  Vascular tissues are discolored in this tomato stem as a result of Fusarium crown and root rot.  Note that discoloration only goes a few inches up the stem.  Tomatoes with Fusarium wilt have a similar discoloration that goes up into the canopy of the plant.  


April 18
Fertility for the Southwest Purdue Agricultural Center Tomato Trial

 Last year at the Southwest Purdue Agricultural Center (SWPAC) we conducted a tomato high tunnel trial described here.  In this article, I would like to talk about the trial we will conduct in 2015, a repeat of the 2014 trial.  In particular, I would like to talk about what we have done for fertility. 

Before deciding on a fertility scheme, it is critical to conduct a soil test each year.  Our soil test from November 2014 showed that our high tunnels were low in sulfur, boron and moderately low in zinc.  In fact, plant tissue tests conducted during the 2014 season were low for both sulfur and boron.   As a result of these tissue tests, we added a 10% liquid boron product and ammonium thiosulfate (7%) to the fertigation during the 2014 season. However, the next set of tissue tests carried out during the 2014 season also came back low in these two elements.  It wasn’t until the end of the 2014 season that we observed levels of boron and sulfur close to normal.  It may be that when tomato plants are growing very quickly, it is difficult to add sufficient nutrients to keep up with demand. (I should add that our yields of tomatoes were over 140,000 lbs on a per acre basis for the 2014 season.  The low boron and sulfur tissue tests didn’t seem to hurt our yields too much.  However, if we hadn’t monitored by tissue tests and added boron and sulfur, the yield may have been affected.) Since we had trouble keeping up with boron and sulfur levels in 2014, this year we decided to add 2.5 lbs per acre of zinc sulfur (10/7%) and 1.5 lbs. per acre boron (14.3%) pre-plant broadcast.  We also added 200 lb per acre pelletized lime. 

During the season we will add nutrients at every irrigation (fertigation).  We transplanted on April 2, 2015, adding a cup of 20-20-20 liquid starter fertilizer per plant.  We started fertigating potassium nitrate (KNO3) on April 6.  We mix 2 oz. of KNO3 per gallon which is then applied at a ratio of 1:100 at each fertigation.  Each high tunnel has 5 rows 80 feet long that has drip tape and black plastic mulch.  We started out fertigating 20 gallons twice a day per high tunnel.  Five days later, we started fertigating 20 gallons 3 times a day. On April 21, we started giving the tomatoes 30 gal 3 times per day.  

We try to avoid fertigating with pre-mixed products such as a 20-20-20 through the drip.  Such products almost invariably add elements that are not needed.  In our case, for example, phosphate is not needed and would be added in most general mixes. Adding elements that are not needed may lead to a buildup of salts in the soil.  This is a particular problem where tomatoes are grown year after year in a greenhouse or high tunnel. 

Please return to this blog to hear about other developments in our high tunnel projects or other vegetable issues that I encounter during the season.  And feel free to contact me with questions or comments.  

April 15
Watermelon Fungicide application Schedule

Below I have written some hints on how to develop a watermelon fungicide application schedule.  When I presented this at the University of Kentucky this winter I promised to post this  So, I am late.  Remember, do not wait until symptoms of disease develop.  Keep a regular schedule.  Be sure to have an official diagnosis of any symptoms you are not sure of.  To help watermelon growers apply fungicides according to the weather, Dr. Rick Latin at Purdue Unviersity developed MELCAST, a weather-based disease-forecasing system.  

Figure 1:  This diagram shows a possible fungicide schedule for watermelon.  Here, the contact fungicide with the active infredient chlorothalonil or mancozeb are used all season long.  Since both of these active ingredeints have the FRAC code M, there is no need to alternate to a different mode of action.  Most chlorothalonil products have a 12 hour re-entry interval (REI)l and a 0 day pre-harvest interval (PHI).  Most mancozeb products have a 48 hour REI and a 5 day PHI.  

Figure 2:  In this scheme, contact fungicides such as used above are used for most of the season (red arrows), but relatively more expensive systemic fungicides are suggested from mid to late June.  Note that a contact fungicide is used in-between the use of the systemic fungicides.  It is important not to use fungicides with the same FRAC codes back to back.  I have tried to suggest that the systemics might be used at about lay-by.  That is, at the point where the vines are piled on top of the plastic mulch-just after the last vine turning.  

Figure 3:  Here I suggest that the same systemic fungicide, Pristine, is used with an application of Bravo or some other contact fungides used in between.


.Figure 4:  Here I suggest that two different systemic fungicides may be used back-to-back if they have different FRAC codes, that is if they have different modes of action.  

Some general comments.  Contact fungicides, such as chlorothalonil and mancozeb, are designed so that if applied to foliage in a manner to get good coverage the foliage is protected.  That is, the fungicides covers the foliage and inhibits spores that may be deposited on leaves.  Contact fugncides do not move into the plant.  

Systemic fungicides move into the plant.  But how far the system fungicides moves within the plant depends on the product.  Most do not move more than inch.  Almost all systemic fungicides move toward tip of the plant, not toward the base or roots.  Systemic fungicides may have some efficacy against exisiting disease, but it is still much more effective to apply all fungicides before the disease gets started.  

I have mentioned a few fungicides in particular here, but just as examples.  There may be other fungicides more effective for your purpose  See the Midwest Vegetable Production Guide for Commercial Growers​ for more information.

April 09
Cucurbit Production in Indiana: 1925 and 2013

In December 2014​, I described the ‘Yearbook of Agriculture, 1928”. In that blog, I wrote about processing tomato production in 1925 and 2013 (the ‘Yearbook of Agriculture, 1928’ lists data back to 1925).  Today, I would like to discuss cantaloupe and watermelon production. Unfortunately, yields posted in the “Yearbook” are in different units than in use today. However, I can compare acreage in 1925 and 2015. 

Cantaloupe production in Indiana in 2013 was at 2,100 acres. This compares to 4,820 acres in 1925. Part of the reason for the drop in acres might be that cantaloupe requires a lot of postharvest handling.  Buyers want cantaloupe, also known as muskmelon, to be washed and cooled. Food safety concerns require growers to invest in specialized equipment and wade through reams of regulations.

In 1925, Indiana was number 6 in the US in cantaloupe acreage, behind California and Arizona (of course) as well as Colorado with 7,900, Arkansas with 7,730 and Maryland with 5,570.  The 2013 USDA data, which lists Indiana as number 4, doesn’t even list Arkansas and lists Maryland with 630 acres and Colorado with 600.  It is interesting to note that total acreage for cantaloupe production has dropped from 93,260 in 1925 to 70,410 in 2013. Acreage appears to have consolidated in states like California, Arizona and Indiana.  My guess is that yields per acre have also gone up, but I can’t compare given the units used in 1925. 

I mentioned that production tracked in different units back then.  In 1925, Indiana produced 627,000 ‘crates’ of cantaloupes. I am not sure what a crate is; it may have been in crates of 36-45 cantaloupe.  In any case, an average price per crate in 1915 was $1.29.  If correct that means that cantaloupe were 2 to 3 cents per fruit! 

If one uses the above production data for 1925, then cantaloupe production value in Indiana was $808,830. Figures for 2013 give a value of $11,500,000. Of course, inflation accounts for much of the increase in value.  Whatever the reasons for the increase, the cantaloupe industry in Indiana is healthy. 

Watermelon acreage in Indiana went from 3,440 in 1925 to 7,400 in 2013. It seems that what was lost in cantaloupe acreage has been made up for in watermelon acres. Watermelon do not have the same post-harvest needs as cantaloupe.  In 1925 Indiana was number 8 in the US.  In 2013, Indiana was number 6. A couple of states that Indiana jumped ahead of in the intervening years are Missouri and Alabama with acreage at 12,200 and 10,030, respectively.​

April 03
Updates to the Midwest Vegetable Production Guide, 2015

While the hard copy of the Midwest Vegetable Production Guide for Commercial Growers 2015 (ID-56) has been available since early January, the on-line version is updated as needed. Below I outline the latest changes.

Page 40, Table 16.  Several insecticide products were added to the “Insecticide Labeling for Greenhouse Use” table. 

Page 100, Cucurbit chapter.  Luna Privilege® was removed from the lists of suggested products for Alternaria leaf blight control and gummy stem blight/black rot control. While Luna Privilege is labeled for these uses, it is not available yet.

Page 100, Cucurbit chapter.  The rates for Presidio® for downy mildew and Phytophthora blight control were modified by the manufacturer. 

Page 109, Product/Disease Rating for All Cucurbits.  Several products were deleted, added, or modified in the Product/Disease Ratings for All Cucurbits table.  These include Luna Experience®, Actigard, Revus ® and Presidio®.

Page 125, Fruiting Vegetable Chapter.  Ridomil Gold SL® was added to the list of recommended products for buckeye rot and Phytophthora blight control in tomato.

Page 125, Fruiting Vegetable Chapter.  Gavel 75DF® was added to the list of recommended products for leaf mold control in tomato. 

Page 130, Product/Disease Ratings for All Fruiting Vegetables.  Several products were deleted, added, or modified in the Product/Disease Ratings for All Fruiting Vegetables table.  These include Bravo®, Dithane®, Priaxor®, Quadris Top®, Fontelis® and Inspire Super®

Note that the index page for the on-line version of the ID-56 details the change history.  If you have questions or comments about any of these changes or want a hardcopy of the changes, contact me at or (812) 886-0198


March 08
How many staked tomatoes should I put in my high tunnel?

Over the last several years, the number of questions I have had about tomato production in high tunnels has increased dramatically. Since I am a plant pathologist, most of the questions I have been asked are about diseases of tomatoes in high tunnels. However, I also have been asked production questions. One particular question about tomato product that may impact disease severity is this:  how many staked tomatoes can be grown in a high tunnel effectively?

To be honest, the above question is one that I often ask myself when I observe high tunnels in Indiana. It isn’t necessarily one that is asked by growers. But maybe it should be. It has been my observation that growers often try to place too many staked tomatoes in a high tunnel. The result may include diseased tomato plants due to insufficient air circulation, poor quality fruit and even reduced yields. I was not able to find any information about plant spacing of staked tomatoes in high tunnels. So, I decided to research the subject myself. 

Let me take a moment to insert some definitions. A high tunnel is a greenhouse with passive heating. The only heat is that supplied is from sunshine trapped in the structure during the day. The structure is cooled by raising the sides and/or venting the top. Staked tomatoes are determinant tomatoes that grow only to a specific height. This is in contrast to indeterminate tomatoes that are trellised to the ceiling and back down again indefinitely. The study that I will describe here is for tomatoes that are grown in the ground as opposed to in pots are bags. 

The 2014 staked tomato study

The 2014 study included two varieties at 5 different plant populations. Both varieties, Red Deuce and Mountain Spring are determinant. Each variety was grown at one of 5 different plant in-row spacing’s (plant population): 18 inches-Florida weave, 20 inches-Florida Weave, 20 inches Spanish trellis, 24 inches-Florida weave, 28 inch-Florida weave. In the Florida weave method, a wooden stake was placed every two plants and twine was woven around the plants and stakes to keep the plants upright. The Spanish trellis technique placed 4 stakes around two tomato plants with an X-pattern of twine woven between the stakes. In each case, twine was tied every 8 to 12 inches of plant growth. It is important to realize that although I varied the spacing of plants within a row, I did not vary the width between rows (center-to-center) which remained at 5 feet for all treatments. 

The influence of varieties and plant populations on plant disease

It was my hypothesis that tomato plants grown at narrow spacing’s would have less ventilation, higher humidity and more disease when compared with tomato plants at more  distant spacing’s.  In the first week of August, the disease leaf mold was observed on the tomatoes in the experiment. I took observations of disease every few days.   

While I observed leaf mold on the variety Mountain Spring, I never observed any leaf mold on Red Deuce. This was surprising since Red Deuce was not listed as resistant.  It is always a good idea to choose a variety with host resistance, but also note the disease reaction of your plants regardless of how the variety is listed. 

Regardless of what I thought would happen, I did not observe more disease on varieties at closer spacing’s.  Does this mean that growers should space tomatoes very close together?

I think there are several factors which may have influenced whether the narrow spacing became more diseased.  


  • ·         If I could have planted the entire high tunnel to a narrow spacing, then ventilation/humidity may have been affected by in-row spacing differences. 
  • ·         Center-to-center spacing may be more important in disease management than in-row spacing.  Remember that I did not vary center-to-center spacing. 
  • ·         We use a high tunnel that has a ridge vent.  It is possible that such a high tunnel design reduces relative humidity over a design without ridge vents. 
  • ·        ​ These results were for the disease leaf mold.  Results with other diseases may vary. 


Further, placing tomatoes very close together may have other repercussions—read on. 


The influence of varieties and plant populations on weight and number of tomatoes

Growers might be interested in knowing how these treatments affected the yield in weight and number of fruit. 

Variety-There was no significant difference in the yield in weight between Red Deuce and Mountain Spring when calculated over the entire season. However, there were significantly more Mountain Spring tomatoes than Red Deuce. (I noted earlier here that the Mountain Spring tomatoes had physiological leaf roll. Given the results of this study after one year, it appears that the leaf roll on the Mountain Spring did not hurt the yield.) Red Deuce yielded significantly larger fruit than Mountain Spring. 

Plant populations-There was no difference in the weight of fruit harvested per linear foot when analyzed by plant population when calculated over the entire season. However, the number of fruit per linear foot was less on plants spaced at 24 and 28 inches compared to plants spaced at 20 inches on a Spanish trellis. 

The influence of varieties and plant populations on the mean weight of tomatoes

Many growers are able to obtain a premium for larger tomatoes. So, I also looked at whether the variety and plant population influenced the size of tomatoes. When calculated over the entire season, Red Deuce had larger (heavier) fruit than Mountain Spring.  Perhaps more important, plants at narrow spacing’s tended to have smaller fruit than plants at more distant spacing’s. For example, plants at 16 inches with Florida Weave and 20 inches with Spanish Trellis had significantly larger fruit than plants spaced at either 24 or 28 inches with Florida weave. 

Take Home message

Plant disease-leaf mold disease, while severe on Mountain Spring tomatoes, did not affect Red Deuce tomatoes in this experiment. Plant populations did not influence the amount of leaf mold on tomato plants. 

Yield-I was not able to observe any difference in yield in pounds for tomato fruit when I measured over the entire season. However, I did see more tomato fruit on plants spaced closer together. Mountain Spring had more tomatoes than Red Deuce. 

Mean fruit weight-Growers who are interested in larger tomatoes will want to avoid the closest spacing’s tried here. Plus, Red Deuce had larger tomatoes than Mountain Spring.  



My plan is to repeat this experiment in the summer of 2015. More detailed recommendations will be made when the results of both years of experiments have been analyzed. What follows, however, are my thoughts so far.  The most effective between row spacing (center-to-center) should be about 5 feet.   In-row spacing should be from 20 to 24 inches.  

Watch this space for more information or updates.  ​ 

March 08
White Mold of Tomatoes Observed in Greenhouse

Last week, I observed white mold of recently transplanted tomato plants in a greenhouse situation.  I have described the symptoms, biology and management of white mold here. 

I have never observed white mold (a.k.a, timber rot) in February before. I have observed white mold of tomato transplants in April. However, the very small mushroom (smaller than a dime) that is part of the life cycle usually emerges in the spring after a cold period. 

The appearance of white mold in February may be as a result of the presence of the mushroom in the greenhouse that produced the transplants. 

To reduce severity of white mold of tomato, I recommend that tomato growers:

·         Inspect transplants for stem lesions which may be a symptom of white mold.  Bring questionable symptoms to my attention or send them to the Purdue Plant and Pest Diagnostic Laboratory

·         Clean and sanitize greenhouses in-between tomato transplant generations.

·         Use a floor covering to reduce the chance of crop residue getting in the soil.  A floor covering should also reduce weeds and the white mold mushrooms. 

Contans is a product labeled for greenhouse use.  It must be worked into the soil months before the tomato crop is planted. See the Midwest Vegetable Production Guide for Commercial Growers, 2015 ( ID-56) or see the Contans label for more information. ​ 
White mold, also known as timber rot, on a tomato transplant.  The stem of the seedling has broken at the point of the white mold lesion.  Note the white fungus present on the lesion.  
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February 06
The Midwest Vegetable Production Guide is Now Available

The Midwest Vegetable Production Guide for Commercial Growers 2015 (ID-56) is now available on-line​ and as a hard copy from Purdue University. Please read below for an update to the 2015 version of this guide. 

What’s New in 2015?

Highlights of Changes in This Edition

New and Revised Sections

• Table 33: Common and Scientific Vegetable Pest Names (page 74) lists the common and scientific names of the pests listed in this guide.

• Table 18: Sanitizers Approved for Wash or Process Water (page 46) lists federally approved sanitizers for vegetables.

• Table 12: Yields of Vegetable Crops (page 37) has been updated.

Disease Management

• White rust has been added to the Cole Crops and Brassica Leafy Greens chapter.

• Bacterial fruit botch recommendations have been revised in the Cucurbit Crops chapter. • Merivon® has been added to the Cole Crops and Brassica Leafy Greens, Cucurbit Crops, and Dry Bulb and Green Bunching Onion, Garlic, and Leek chapters.

• Priaxor® has been added to the Fruiting Vegetables chapter.

• Aproach® has been added to the Legumes chapter.

Weed Management

• Command 3ME® is now labeled for use on broccoli, cauliflower, Brussels sprouts (see the Cole Crops chapter), and rhubarb.

• League ® is now labeled for use in pepper, tomato, potato, cantaloupe, and watermelon. The active ingredient is imazosulfuron, an ALS-inhibiting herbicide. This material has pre- and postemergent activity against yellow nutsedge, hairy galinsoga, purslane, and pigweeds, and postemergent activity against morningglory.

 Insect Management

• Azera® was added to the Cole Crops and Brassica Leafy Greens and Cucurbit Crops chapters.

• Beleaf 50SG® was added to the Cole Crops and Brassica Leafy Greens, Cucurbit Crops, Fruiting Vegetables, Potato, and Sweet Potato chapters.

• Exirel® was added to the Cole Crops and Brassica Leafy Greens, Cucurbit Crops, Fruiting Vegetables, and Dry Bulb and Green Bunching Onion, Garlic, and Leek chapters.

• Torac® was added to the Cole Crops and Brassica Leafy Greens and Potato chapters.

• Transform® was added to the Legumes and Potato chapters.

• Zeal® was added to the Mint and Okra chapters.

Updates to the Midwest Vegetable Production Guide-These changes appear in the on-line version of the ID-56.  Please make these changes to your hard copy. 

·      Bravo Weather Stik was removed from the cucurbit powdery mildew management section

·      Merivon was added to the cucurbit powdery mildew management section. 


​​ ​

January 09
Bacterial Fruit Blotch Update

Bacterial fruit blotch is a disease that can affect most cucurbits. However, the symptoms are most often observed on watermelon. A brief description of this disease and some photos can be found here. This article will introduce new recommendations for this disease in Indiana. Details of these recommendations can be found in the Midwest Vegetable Production Guide for Commercial Growers 2015 (ID-56). Hard copies of the ID-56 are available from Purdue University now for $10. A free on-line version of the ID-56 will be available soon at

Copper products such as those with copper hydroxide or copper sulfate are often recommended for management of bacterial fruit blotch (BFB).  However copper products applied too often can cause yellowing of leaves and even yield loss (phytotoxicity). Since BFB is mostly caused by rare contaminated seed lots, I have been reluctant to recommend copper products routinely for watermelon growers. However, the last few years I have observed several growers suffer large losses from this disease. Therefore, I have decided to bring Indiana recommendations in line with those of Georgia and South Carolina. See below.

Instead of applying copper products all season long, apply copper 2 weeks before first female bloom, at first female bloom and 2 weeks after first female bloom. Additionally, application of the product Actigard at 2 of the 3 copper application times listed above is recommended. 

Actigard does not have any direct effect on the bacterium that causes BFB.  Instead, Actigard ‘tells’ the plant that it is under attack from a disease, causing the plant to produce defense compounds.  Like copper compounds, Actigard can cause yield losses in plants.  Therefore, do not use Actigard on plants that have been stressed by weather or other factors.  I would use the low rate of Actigard, 0.5 oz. per acre.  

If you have any questions or comments about bacterial fruit blotch, these new recommendations or the Midwest Vegetable Production Guide for Commercial Growers 2015 (ID-56), please do not hesitate to contact me. ​ 

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 About this blog


Dan Egel is an extension plant pathologist with Purdue University who works with vegetable growers across the state of Indiana. This blog will highlight recent disease issues, management options, meeting dates and new publications relevant to vegetable growers. Dan is located just north of Vincennes at the Southwest Purdue Agricultural Center.


Contact Information

Dan Egel
Southwest Purdue Agricultural Program
4369 N. Purdue Road
Vincennes, IN 47591
Phone: 812-886-0198

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