Watermelon

Alternaria leaf blight

Figure 1. Alternaria leaf blight on watermelon.

Figure 2. Alternaria leaf blight of watermelon photo showing lesion structures.

Anthracnose of Watermelon

Figure 1. Anthracnose lesion on watermelon transplant. Note angular, jagged lesion.

Figure 2. Anthracnose lesions on the hypocotyl of these watermelon transplants has caused the plants to wilt.

Figure 3. Anthracnose lesion on several watermelon transplants. Lesions are primarily on cotyledons (seed leaves).

Figure 4. Anthracnose of watermelon occasionally cause lesions on the hypocotyl, between the cotyledon and the soil.

Figure 5. Anthracnose lesions on mature watermelon leaves tend to be angular and jagged.

Figure 6. Another photo of anthracnose of watermelon on a leaf. Note the yellow color on the margin of the lesions.

Figure 7. Several anthracnose lesions on a watermelon leaf.

Figure 8. A close-up of a lesion of anthracnose on a watermelon leaf. Note the sharp, angular shape of the lesion.

Figure 9. A watermelon fruit with pit-like lesions of anthracnose. Note the orange or salmon-like color of the lesions due to the color of the spores.

Figure 10. A close-up of a lesion of anthracnose on a watermelon fruit.

Figure 11. The anthracnose lesions on this watermelon fruit appear more as cracks than pit-like as in other photos. Note that there is still a hint of orange in some of the cracks due to the spore colors. Note also that the lesions tend to be toward the bottom of the fruit as is typical.

Angular leaf spot

Figure 1. Angular leaf spot of watermelon includes round, light brown necrotic lesion with chlorotic halo.

Figure 2. Angular leaf spot on watermelon leaf has caused dark, necrotic lesion on cotyledon.

Figure 3. Several watermelon transplants have lesions of angular leaf spot.

Bacterial fruit blotch

Figure 1. An irregular dark lesion can be observed on the top of this watermelon fruit caused by bacterial fruit blotch of watermelon.

Figure 2. Watermelon is cracked probably due to secondary infection of a lesion of bacterial fruit blotch. Note leakage of fluids has dripped down side of fruit.

Figure 3. A large, spreading lesion due to bacterial fruit blotch is seen on the top of this watermelon. Note cracking of lesion.

Figure 4. Leaf lesions of bacterial fruit blotch of watermelon may be irregular.

Figure 5. Leaf lesions of bacterial fruit blotch of watermelon can be irregular.

Figure 6. Lesion of bacterial fruit blotch of watermelon seedling.

Black root rot

Figure 1. The symptoms of wilt in this watermelon could be from many causes. Black root rot can cause wilt such as seen here.

Figure 2. Dark areas on the hypocotyl of this watermelon seedling is caused by chlamydospores (resting spores) of the fungus that causes black root rot (Thielaviopsis basicola).

Figure 3. Dark discoloration and poor root system are as a result of black root rot of watermelon.

Figure 4. The structures seen here in root tissue are specialized spores known as chlamydospores. These spores are resilient resting spores that help the fungus survive for long periods in the soil. In addition, these spores impart a dark appearance to tissue.

Figure 5. The watermelon seedlings in this transplant tray are declining due to black root rot.

Figure 6. The watermelon transplants in the tray above are declining due black root rot which can be seen causing dark symptoms here on the hypocotyl.

Figure 7. This watermelon is affected by gummy stem blight immediately below and above the cotyledon, black root rot at the lower hypocotyl and root knot nematodes on the roots.

Cercospora spot

Figure 1. Cercospora leaf spot on watermelon.

Figure 2. Closeup of Cercospora leaf spot on watermelon.

Chimera

Figure 1. Watermelon with irregular color patterns due to a chimera, also known as a somatic mutation.

Figure 2. Chimera has caused irregular patterns on a watermelon leaves.

Figure 3. A chimera in a watermelon leaf.

Figure 4. Chimera on a watermelon transplant.

Damping-of

Figure 1. Damping off of watermelon.

Figure 2. Damping off of watermelon.

Figure 3. Damping off of watermelon.

Figure 4. Damping off of watermelon.

Dodder

Figure 1. Dodder on watermelon.

Figure 2. Dodder on watermelon.

Downy mildew

Figure 1. Chlorotic lesions of downy mildew on a watermelon leaf. Note that a few of the lesions are starting to become necrotic.

Figure 2. Chlorotic and necrotic lesions on watermelon leaf.

Figure 3. Underside of watermelon leaf with downy mildew. Note sporulation of downy mildew-see red arrows.

Figure 4. Severe outbreak of downy mildew on watermelon. Note that stem and fruit of watermelon are not directly affected.

Fusarium wilt

Figure 1. Fusarium wilt of watermelon often causes one vine to wilt while the rest of the plant appears unaffected. Symptoms of this disease often begin when plants are just starting to vine.

Figure 2. Vascular discoloration present in lower stem may be a symptom of Fusarium wilt of watermelon. Note that one-sided vascular discoloration in the stem may correspond to one-sided wilt in plant.

Figure 3. The distribution of Fusarium wilt of watermelon in the field is often clustered.

Figure 4. Early symptoms of Fusarium wilt in watermelon include wilt of almost all leaves. Note coloration of wilted leaves.

Figure 5. One sided wilt of watermelon leaf. Note also that older leaves usually wilt before young leaves.

Figure 6. Seedling distribution of Fusarium wilt in watermelon may be randomly distributed in transplant trays.

Figure 7. Distribution of Fusarium wilt of watermelon in transplant trays may be clustered under some circumstances.

Figure 8. Hypocotyl has collapsed and become necrotic due to Fusarium wilt in watermelon at the transplant stage. Note pink-like sporulation of Fusarium fungus at top of hypocotyl.

Figure 9. Close-up of hypocotyl of watermelon seedling infected with Fusarium wilt.

Figure 10. When Fusarium wilt in watermelon occurs in late season, wilt and collapse of vines such as seen here in the foreground may occur.

Figure 11. Vascular discoloration in Fusarium wilt of watermelon in a late season production.

Figure 12. Fusarium wilt of watermelon in this late season field has caused some of the vines to become necrotic while some vines remain apparently healthy.

Gummy stem blight

Figure 1. Gummy stem blight causes dark, amorphous, necrotic lesions on watermelon leaves.

Figure 2. Gummy stem blight lesions on watermelon leaves sometimes have a ring-like structure.

Figure 3. Underside of a watermelon leaf with a gummy stem blight lesion.

Figure 4. Large gummy stem blight lesion along the midrib of a watermelon leaf

Figure 5. Close up of gummy stem blight lesions on a watermelon leaf, one lesion with a shot-hole.

Figure 6. Lesion of gummy stem blight on a watermelon leaf petiole.

Figure 7. Lesion of gummy stem blight on a watermelon stem. The brown ooze or gum does not always occur in association with this disease and many other diseases and injuries to the stem may cause such an ooze.

Figure 8. Fruiting bodies, pycnidia, on a watermelon leaf petiole.

Figure 9. A field of watermelon with a severe outbreak of gummy stem blight manifested by defoliation and numerous lesions.

Lightning Damage

Figure 1. Lightning damage on watermelon. Note wilt and other damage.

Figure 2. Lightning damage on watermelon. Note approximately round area of damage. This photos was taken a few days after the strike occurred.

Figure 3. Lightening damage on watermelon. Note wilt and leaf burn.

Figure 4. Lightning damage on watermelon. Note wilt and leaf burn.

Figure 5. Lightning damage on watermelon.

Figure 6. Lightning damage on weeds in watermelon field.

Phytophthora blight

Figure 1. Phytophthora blight has caused the round bruised-like areas on the watermelon.

Figure 2. Phytophthora blight has caused the water-soaked symptoms on the base of this watermelon including the white sporulation of the fungus.

Figure 3. Phytophthora blight of watermelon has caused the large necrotic regions on this watermelon. The vines of watermelon are usually not affected by Phytophthora blight, but in extreme cases can become symptomatic.

Figure 4. Phytophthora blight of watermelon has caused the lesions with gray/white sporulation. Note the bruised circular areas around each lesion.

Powdery mildew

Figure 1. Leaf lesions of powdery mildew of watermelon may be white due to the sporulation of the fungus or colonies on the reverse of the leaf may show up chlorotic.

Figure 2. Leaf with sporulation of powdery mildew.

Figure 3. Powdery mildew of watermelon fruit. (Photo by Wenjinjg Guan.)

Figure 4. Powdery mildew on stem of watermelon.

Root knot nematode

Figure 1. Roots of watermelon many galls due to root knot nematode.

Figure 2. Galls of root knot nematode on watermelon roots.

Figure 3. Root nematode galls on a watermelon root system that has been washed to reveal symptoms of root knot.

Figure 4. A watermelon seedling that has been recently transplanted in the field has root knot galls visible. Note that symptoms of decline of the plant foliage are visible.