Current Events in Commercial Vegetable Production

 Below is an article about vegetable disease, a new article will appear periodically.


October 31, 2013

Pesticides are designed to help growers manage insects, diseases and weeds. However, under some circumstances, pesticides may result in plant damage or phytotoxicity. That is, it is possible that the proper use of a pesticide may result in plant damage. Although it is impossible to anticipate every instance of phytotoxicity, pesticide companies have gone to a lot of trouble to find as much as possible about possible phytotoxic interactions of pesticides and plant. Such phytotoxic interactions of pesticides and plants are placed in the pesticide label so that growers may avoid uses that may cause problems.  This article gives some examples of phytotoxic interactions of pesticides that are listed clearly on the label.  A thorough reading of the pesticide label will help to avoid possible problems.

Phytotoxicity of pesticides can be roughly grouped into 3 categories. The first is pesticide interactions that occur as a result of mixing particular pesticides. In such cases, proper application of individual pesticides has good results. However, mix these two pesticides together and plant damage can result. Our example is the mixing of Quadris® and Lannate® together for application on cucurbits. The exact language of the Quadris® label is: do not tank mix Quadris® with Malathion®, Kelthane®, Thiodan®, Phaser®, Lannate®, Lorsban®, M-Pede® or Botran®. A recent report of the use of Quadris® and Lannate® causing phytotoxicity on watermelon confirms the wisdom of this language.

A second type of pesticide phytotoxicity is variety specific. The application of the fungicide Gavel® to certain cantaloupe varieties is our example. The exact language of the Gavel® label is: some cantaloupe varieties (i.e., Harvest Queen, Gold Star, Super Star, Sweet and Early, and Saticoy) are sensitive to Gavel®. Again, a close reading of the pesticide label will avoid a lot of trouble.

The third type of phytotoxicity is plant stage specific. Our example comes from the Bravo Weatherstik® label. The label states: Spraying mature fruit may result in sunburn of the upper surface of the fruit. The label then lists several specific conditions under which sunburn may result including ‘intense sunlight and heat’. That is, application of Bravo® to mature fruit under specific conditions may result in sunburn. Growers will have to decide whether these specific conditions may exist. 

Because phytotoxicity doesn’t always occur, it may be tempting to think that if no problems were observed in one instance, the instructions on the label are overly cautious. But the warnings on pesticide labels exist for a reason–it is very probable that eventually the damage warned about will occur. Furthermore, pesticide labels are not just friendly reminders. The label is the law. 

If you have questions about pesticides and possible phytotoxic reactions, please give a Purdue University Extension specialist a call.


Past Articles

Pesticides and Phytotoxicity (PDF), 10-31-13

Downy Mildew (PDF), 8-8-13

Powdery Mildew on Cantaloupe (PDF), 7-25-13

Phytophthora Blight of Cucurbits (PDF), 7-25-13

Black Rot of Cabbage and Other Crucifers (PDF), 7-11-13

Bacterial Spot of Tomato and Pepper (PDF), 5-16-13

Blossom End Rot of Fruiting Vegetables (PDF), 5-2-13

Cucurbit Transplant Disease (PDF), 5-2-13

Pith Necrosis VS Bacterial Canker: A Tale of Two Tomato Diseases (PDF), 4-18-13

Vegetable Disease in Greenhouses (PDF), 4-4-2013 

Anthracnose of Pumpkin (PDF), 9-28-2012