Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
The excessively hot and dry weather is taking its toll on dryland field crops. While most vegetables are irrigated, we are still seeing heat and drought related problems. Some common problems are:
Sunscald
Sunscald is evident on many vegetables. This is especially the case where irrigation has not been able to keep up and plants have wilted for a period of time, exposing fruits. Dark colored fruits are most susceptible. Sunscald is most common on peppers, tomatoes, and cucumbers but also can be seen on watermelons, melons, and some squash. Exposed potato tubers are also susceptible. Sunscald is controlled by not allowing plants to wilt and having adequate leaf cover.
Blossom End Rot
Blossom end rot on peppers and tomatoes is common at this time due to the inability of plants to move enough calcium into expanding fruits, especially if plants are water stressed for periods of time. Blossom end rot increases in excessively hot weather. Blossom end rot can be reduced by addition of soluble calcium containing fertilizers and by irrigating so that plant demands are being met.
Leaf Curl
Plants such as tomatoes, peppers, and potatoes often react to hot weather by having increased amount of permanent leaf curling. No control measures are necessary.
Leaf Scorch
Leafy vegetables under heat and water stress often will have leaf edges that scorch. This also can be compounded by calcium deficiencies or reduction in calcium movement to the edges of rapidly expanding leaves. Many other vegetables will show leaf scorch symptoms. Having adequate irrigation management is critical to avoiding leaf scorch. Evaporative cooling from overhead irrigation can also help reduce leaf scorch.
Transplant Collapse
Late transplanted vegetables on black plastic mulch can collapse due to heat necrosis of stems touching the plastic mulch or by overheating of beds under the plastic so that roots are killed. Control by using white plastic mulch instead of black, using a larger planting hole to dissipate the excess heat, running overhead irrigation to cool the mulch, and keeping beds moist with drip irrigation.