Plant Diseases Management

As soybeans begin the pod fill growth stages, heat and drought stresses can trigger the development of many disease symptoms. Currently we are seeing many instances of stem diseases in soybean. Many pathogens are associated with stem diseases in soybean, and many produce very similar foliar symptoms, which is why diagnosis from foliar symptoms alone typically leads to a misdiagnosis. Submit questionable samples to the UMD Plant Diagnostic Lab for proper identification. Common soybean stem diseases and their symptoms/signs are outlined below.

Tomatoes are grafted by joining the top part of one plant (the scion) to the root system of another plant (the rootstock) (fig. 1). The resulting plant is usually more vigorous and productive.

I do not have to tell you that these frequent and heavy rains we have been having over the last 2-3 weeks have really increased the amount of foliar and at times soil diseases in our vegetable crops. In cucurbits foliar diseases such as Alternaria, gummy stem blight and an odd one Cercospora (figs 1a, 1b) all have been found causing moderate to severe defoliation in some fields that are heavy with fruit.

In the last week tomatoes from different counties in Maryland were found with the same unusual disease symptoms, called tomato pith necrosis. All the problem tomatoes were from early planted fields. Tomato pith necrosis is caused by the soilborne bacterium Pseudomonas corrugata. It has occurred infrequently in Maryland over the past few decades. The disease usually is found in early planted tomatoes when night temperatures are cool, but the humidity is high, and plants are growing too rapidly because of excessive nitrogen application.

Gummy stem blight (GSB) was found in an Eastern shore muskmelon field in the last few weeks. It is a cucurbit disease caused by the fungal pathogen Didymella bryoniae. This fungus is favored by cool to warm, rainy weather. It can infect a host at any stage of growth and affects almost all parts of the plant including leaves, stems and fruits.

To no one’s surprise this week has seen a great number of problems pop-up in tomato fields throughout our area. The first of course has been disease with bacterial and fungal diseases spreading. The fungal pathogens usually can be contained with timely (as difficult as that is) fungicide applications. Bacterial spot or speck on the other hand can be much more difficult to control once it gets started and the weather remains wet and warm. In figure 1 on the right hand side is a row of tomatoes that had been sprayed with fungicides and copper for the last several weeks. Bacterial spot has ravaged this row.

Using Silicon, Stimplex and Plant Resistance in Pumpkin Production Systems to Reduce Plant Disease Loss

Severe outbreaks of downy mildew in garden impatiens (Impatiens walleriana) were reported first reported in the fall of 2011 on landscape plantings in Europe as well as in the US (Northeast, Midwest). In Maryland, the Plant Diagnostic Lab received its first infected sample in early June 2012. If you grow garden impatiens, it is important to be on the lookout for this disease.

I recently received an inquiry from a high tunnel grower about unusual symptoms on tomato leaves.

Fruit and Vegetable News, Volume 12, Issue 3 (June 10, 2021)