For over a decade, basil downy mildew (BDM) has caused significant losses in basil grown in organic and conventional field and greenhouse production across the United States. At the time of its introduction, there were very few fungicides labeled for its control making it nearly impossible to grow a successful crop in many areas of the country. [Read more…]
July 2, 2022 Andy Wyenandt
Vegetable Disease Update: 07-02-22
- Powdery mildew has been reported in cucurbit crops. For more information on the control of CPM please click here.
- Cucurbit downy mildew has been reported on cucumber in southern New Jersey and Eastern PA. For more information on CDM control please click here.
- Bacterial leaf spot has been reported in pepper. More more information on BLS control please click here.
- Bacterial canker has been reported in tomato. For more information on diagnosing important tomato diseases please click here.
- Early blight has been reported on potato.
- Phytophthora blight has been reported on pepper. For more information please click here.
- Dickeya dianthicola has been reported in potato in Virginia and Massachusetts.
- The 2022/2023 Commercial Vegetable Production Recommendations Guide is available for free online or for sale in hardcopy form at many County offices.
- For a quick review on managing fungicide resistance development using tank mixes and fungicide rotations, and information on FRAC group 4, FRAC group 7, and FRAC group 3 and FRAC group 11 fungicides please click on hyperlinks.
July 1, 2022 Andy Wyenandt
Identifying white mold in tomato production
White mold, or timber rot, is caused by the soil-borne fungal pathogen, Sclerotinia sclerotiorum.
High tunnel tomato plant with main stem infected by white mold.
The photo on right shows a high tunnel tomato plant with main stem infected by white mold. Over time the entire plant will slowly collapse looking similar to a wilt or root rot pathogen as the water supply is cut off to the plant.
White mold is common and once introduced into a field or high tunnel it can very difficult to control. The pathogen produces black sclerotia on the surface and inside infected stems. Sclerotia, if they make their way back into the soil, can survive for years causing significant problems.
Infected stems will turn a light brown color and dry up becoming brittle. If the main stem is infected the entire plant will collapse looking like a wilt or root rot issue.
Under hot, humid conditions white fungal growth will develop on the surface of the stems and in some cases sclerotia will develop on the outside of the stem. Breaking open the stem will reveal numerous black sclerotia.
All infected plants and or plant material need to be removed immediately and disposed of properly. Preventative protectant fungicide programs beginning at flowering will help control white mold. Cool, wet weather and poor air circulation favors disease development.
There are a number of control options for conventional and organic growers listed in Table E-11 in the 2022/2023 mid-Atlantic Commercial Vegetable Production Recommendations Guide.
Tomato stem infected by white hold. Note the fungal growth on the surface of the stem.
White mold of tomato. Note the black sclerotia developing inside the brittle stems.
June 30, 2022 Andy Wyenandt
Recognizing Angular Leaf Spot in Cucurbits
Angular leaf spot is common in New Jersey and the region. It often shows up during cooler, wet weather and isolated rain.
Symptoms of angular leaf spot in cucurbit.
Angular leaf spot of pumpkin. Note leaf ‘shot holes’.
Angular leaf spot will first appear as, small water-soaked lesions which will expand until they reach a larger leaf vein resulting in the angular looking symptoms on leaves. Under heavy disease pressure, the bacteria will infect fruit causing small, water-soaked circular spots. In many cases once weather conditions become dry again, infected tissue in leaves will die and fall out leaving the characteristic ‘shot hole’ symptoms. Control of angular leaf spot begins with the application of labeled rates of fixed copper plus mancozeb to help suppress the spread of the disease until hot, dry weather returns.
June 29, 2022 Andy Wyenandt
Preparing for Anthracnose and Alternaria Leaf Blights in Cucurbit Crops
Anthracnose and Alternaria leaf blight can become problematic in cucurbit crops during long periods of wet, humid weather. Both can cause significant losses if not controlled properly. With the production season in full swing, now is a good time to review a few of these important diseases. [Read more…]
June 28, 2022 Andy Wyenandt
Don’t Rely on Disinfestants for Disease Control
The hot, then windy, then wet weather these past few weeks have brought with it prolonged windy days and rain to many areas. In general, this type of weather is ideal for the development and spread of many vegetable diseases.
By now most growers are on weekly protectant fungicide programs to help prevent disease development. It’s important to remember at this point in the season when disease pressure is high that growers stick with their standard fungicide programs.
Growers should not replace fungicides with disinfestant-type products in their weekly fungicide programs.
Remember, disinfestants only kill what they come into direct and immediate contact with and do not offer any residual activity like fungicides do. Disinfestants should be used in conjunction with weekly fungicide programs and be applied based on specific weather events such as following rainfall or overhead irrigation or after certain cultural practices such as tying or pruning where plant injury or wounding may occur.
