watermelon diseases

Alternaria leaf blight

Alternaria leaf blight on watermelon Figure 1. Alternaria leaf blight on watermelon.
Alternaria leaf blight Figure 2. Alternaria leaf blight of watermelon photo showing lesion structures.

Angular leaf spot

 Angular leaf spot of watermelon includes round, light brown necrotic lesion with chlorotic halo. Figure 1. Angular leaf spot of watermelon includes round, light brown necrotic lesion with chlorotic halo.
Angular leaf spot on watermelon leaf has caused dark, necrotic lesion on cotyledon. Figure 2. Angular leaf spot on watermelon leaf has caused dark, necrotic lesion on cotyledon.
Several watermelon transplants have lesions of angular leaf spot. Figure 3. Several watermelon transplants have lesions of angular leaf spot.

Anthracnose

Anthracnose of Watermelon Figure 1. Anthracnose lesion on watermelon transplant. Note angular, jagged lesion.
Anthracnose lesions on watermelon Figure 2. Anthracnose lesions on the hypocotyl of these watermelon transplants has caused the plants to wilt.
Anthracnose lesion on several watermelon transplant Figure 3. Anthracnose lesion on several watermelon transplants. Lesions are primarily on cotyledons (seed leaves).
Anthracnose of watermelon Figure 4. Anthracnose of watermelon occasionally causes lesions on the hypocotyl, between the cotyledon and the soil.
Anthracnose lesions on mature watermelon leaves Figure 5. Anthracnose lesions on mature watermelon leaves tend to be angular and jagged.
 anthracnose of watermelon on a leaf Figure 6. Another photo of anthracnose of watermelon on a leaf. Note the yellow color on the margin of the lesions.
Several anthracnose lesions on a watermelon leaf. Figure 7. Several anthracnose lesions on a watermelon leaf.
Anthracnose 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.
 A watermelon fruit with pit-like lesions of anthracnose 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.
anthracnose on a watermelon fruit. Figure 10. A close-up of a lesion of anthracnose on a watermelon fruit.
anthracnose lesions 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.

Bacterial fruit blotch

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.
Bacterial fruit blotch 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.
Bacterial fruit blotch Figure 3. A large, spreading lesion due to bacterial fruit blotch is seen on the top of this watermelon. Note cracking of lesion.
Leaf lesions of bacterial fruit blotch of watermelon Figure 4. Leaf lesions of bacterial fruit blotch of watermelon may be irregular.
 Leaf lesions of bacterial fruit blot Figure 5. Leaf lesions of bacterial fruit blotch of watermelon can be irregular.
Lesion of bacterial fruit blotch of watermelon Figure 6. Lesion of bacterial fruit blotch of watermelon seedling.

Black root rot

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.
Black root rot 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).
Black root rot Figure 3. Dark discoloration and poor root system are as a result of black root rot of watermelon.
Black root rot 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.
Black root rot Figure 5. The watermelon seedlings in this transplant tray are declining due to black root rot.
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.
Black root rot 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

 Cercospora leaf spot on watermelon Figure 1. Cercospora leaf spot on watermelon.
 Cercospora leaf spot on watermelon Figure 2. Closeup of Cercospora leaf spot on watermelon.

Chimera

Chimera of watermelon Figure 1. Watermelon with irregular color patterns due to a chimera, also known as a somatic mutation.
Chimera of watermelon Figure 2. Chimera has caused irregular patterns on a watermelon leaves.
Chimera of watermelon Figure 3. A chimera in a watermelon leaf.
Chimera on a watermelon transplant. Figure 4. Chimera on a watermelon transplant.

Cross-stitch

Cross-stitch Figure 1. Cross stitch on watermelon.

Damping-off

Damping off of watermelon. Figure 1. Damping off of watermelon.
Damping off of watermelon. Figure 2. Damping off of watermelon.
 Damping off of watermelon. Figure 3. Damping off of watermelon.
 Damping off of watermelon. Figure 4. Damping off of watermelon.

Dodder

Dodder on watermelon. Figure 1. Dodder on watermelon.
Dodder on watermelon. Figure 2. Dodder on watermelon.
Dodder on watermelon. Figure 3. Dodder on watermelon.

Downy mildew

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.
Downy mildew Figure 2. Chlorotic and necrotic lesions on watermelon leaf.
Downy mildew Figure 3. Underside of watermelon leaf with downy mildew. Note sporulation of downy mildew-see red arrows.
Downy mildew Figure 4. Severe outbreak of downy mildew on watermelon. Note that stem and fruit of watermelon are not directly affected.

Fusarium wilt

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.
Fusarium wilt of watermelon 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.
Fusarium wilt of watermelon Figure 3. The distribution of Fusarium wilt of watermelon in the field is often clustered.
 Early symptoms of Fusarium wilt in watermelon Figure 4. Early symptoms of Fusarium wilt in watermelon include wilt of almost all leaves. Note coloration of wilted leaves.
Fusarium wilt Figure 5. One sided wilt of watermelon leaf. Note also that older leaves usually wilt before young leaves.
 Fusarium wilt in watermelon Figure 6. Seedling distribution of Fusarium wilt in watermelon may be randomly distributed in transplant trays.
 Fusarium wilt in watermelon Figure 7. Distribution of Fusarium wilt of watermelon in transplant trays may be clustered under some circumstances.
 Hypocotyl has collapsed and become necrotic due to Fusarium wilt 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.
watermelon seedling infected with Fusarium wilt. Figure 9. Close-up of hypocotyl of watermelon seedling infected with Fusarium wilt.
 Fusarium wilt in watermelon 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.
Fusarium wilt of watermelon Figure 11. Vascular discoloration in Fusarium wilt of watermelon in a late season production.
 Fusarium wilt of watermelon 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

Gummy stem blight Figure 1. Gummy stem blight causes dark, amorphous, necrotic lesions on watermelon leaves.
 Gummy stem blight Figure 2. Gummy stem blight lesions on watermelon leaves sometimes have a ring-like structure.
gummy stem blight lesion. Figure 3. Underside of a watermelon leaf with a gummy stem blight lesion.
 gummy stem blight Figure 4. Large gummy stem blight lesion along the midrib of a watermelon leaf
gummy stem blight Figure 5. Close up of gummy stem blight lesions on a watermelon leaf, one lesion with a shot-hole.
 Lesion of gummy stem blight Figure 6. Lesion of gummy stem blight on a watermelon leaf petiole.
gummy stem blight 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.
gummy stem blight Figure 8. Fruiting bodies, pycnidia, on a watermelon leaf petiole.
 gummy stem blight Figure 9. A field of watermelon with a severe outbreak of gummy stem blight manifested by defoliation and numerous lesions.

Lightning Damage

Lightning damage on watermelon Figure 1. Lightning damage on watermelon. Note wilt and other damage.
 Lightning damage on watermelon Figure 2. Lightning damage on watermelon. Note approximately round area of damage. This photos was taken a few days after the strike occurred.
Lightening damage on watermelon Figure 3. Lightening damage on watermelon. Note wilt and leaf burn.
Lightning damage on watermelon. Figure 4. Lightning damage on watermelon. Note wilt and leaf burn.
Lightning damage on watermelon. Figure 5. Lightning damage on watermelon.
Lightning damage on watermelon. Figure 6. Lightning damage on weeds in watermelon field.

Manganese toxicity

Manganese toxicity Figure 1. Manganese toxicity on watermelon. Note symptomatic vines are clustered in areas of low soil pH.
Manganese toxicity on watermelon. Figure 2. Manganese toxicity on watermelon.
Manganese toxicity on watermelon. Figure 3. Manganese toxicity on watermelon.

Phytophthora blight

Phytophthora blight Figure 1. Phytophthora blight has caused the round bruised-like areas on the watermelon.
Phytophthora blight Figure 2. Phytophthora blight has caused the water-soaked symptoms on the base of this watermelon including the white sporulation of the fungus.
Phytophthora blight 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.
Phytophthora blight Figure 4. Phytophthora blight of watermelon has caused the lesions with gray/white sporulation. Note the bruised circular areas around each lesion.

Powdery mildew

 Leaf lesions of 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.
 Leaf with sporulation of powdery mildew. Figure 2. Leaf with sporulation of powdery mildew.
Powdery mildew of watermelon Figure 3. Powdery mildew of watermelon fruit. (Photo by Wenjing Guan.)
Powdery mildew on stem of watermelon. Figure 4. Powdery mildew on stem of watermelon.

Rind Necrosis

Rind necrosis of watermelon Figure 1. Rind necrosis of watermelon
 Rind necrosis of watermelon Figure 2. Rind necrosis of watermelon
Rind necrosis of watermelon Figure 3. Rind necrosis of watermelon
Severe rind necrosis of watermelon Figure 4. Severe rind necrosis of watermelon

Root knot nematode

Root knot nematode Figure 1. Roots of watermelon with galls due to root knot nematode.
root knot nematode Figure 2. Galls of root knot nematode on watermelon roots.
Root nematode galls on a watermelon root system Figure 3. Root nematode galls on a watermelon root system that has been washed to reveal symptoms of root knot.
root knot nematode 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.
root knot nematode Figure 5. Close up of watermelon roots of transplant with galls.
Root knot nematode Figure 6. Severe root knot nematode galls on watermelon roots.

Target cluster

Target cluster Figure 1. Target cluster of watermelon. Positive for potyvirus.
Target cluster of watermelon. Figure 2. Target cluster of watermelon. Negative for potyvirus.
Target cluster of watermelon. Figure 3. Target cluster of watermelon. Positive for papaya ringspot virus.
Target cluster Figure 4. Target cluster of watermelon. Not analyzed for virus.

Virus

Virus Figure 1. Papaya ringspot virus of watermelon.
Virus Figure 2. Papaya ringspot virus of watermelon.
Virus Figure 3. Watermelon leaf positive for potyvirus.

White mold

 White mold Figure 1. White mold of watermelon
 White mold Figure 2. White mold of watermelon
White mold of watermelon Figure 3. White mold of watermelon.