If you see yellow spots that spread to fill the spaces between leaf veins, your melon or squash plants may have cucurbit yellow stunting disorder. Cucurbit yellow stunting disorder (CYSD or CTSDV) is a viral disease of cucurbits carried by whiteflies.
Cucurbits are popular garden plants. They include summer squash, winter squash, watermelon, muskmelons, pumpkins, cucumbers, and more. Since some whitefly species can travel relatively long distances, this disease can find your garden throughout the growing season. To reduce the chances of the infection spreading from one plant to another, it is a good idea to learn how to recognize this disease in its earliest stages.
The first symptoms of CTSD look much like water stress, as the virus begins spreading throughout the plant. Then, yellow spotting on older leaves will develop. Or, this yellow spotting may mean the plant has a molybdenum deficiency or has cucurbit aphid-borne yellow virus (CABYV). You can take a leaf sample to your nearest county farm advisor, where they will conduct a molecular test to verify the disease.
If the chlorotic areas spread to the point that the entire leaf is yellow, except for the veins, it is likely to be CYSD. Small green patches may appear in the yellow areas. Other symptoms include leaves curling upwards and becoming brittle. As the virus spreads through the plant's vascular system, older leaves start to fall off, and fruit development slows or stops. Fruits that do occur are smaller, less flavorful, and more prone to pests and other diseases. Also, fruits from infected plants do not store as well as fruits from healthy plants.
There are no chemical or biological treatments for this disease. Controlling whiteflies is critical to halting the spread of cucurbit yellow stunting disorder. These tips can help reduce the chances of CYSD spreading through your garden:
• Only use high-quality, disease-free seeds.
• Quarantine and carefully inspect new plants for signs of disease or whiteflies.
• Avoid using broad-spectrum pesticides, which kill whitefly predators.
• Use floating row covers over newly planted seeds and seedlings.
• Remove and destroy infected plants.
• Fertilize and irrigate established plants properly to keep them healthy.
• Employ crop rotation.
Protect your cucurbits from whiteflies for an abundant harvest this summer and fall!
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