Plant Fungal Diseases

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.

Another disease we might be seeing now and in the next week or so is late blight. The weather conditions of the past week have been favorable for its development: cool (for summer temperatures) daytime and nighttime temperatures along with ample moisture.

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.

A very unusual and seldom seen tomato foliar blight was found by an intrepid county educator in Southern Maryland last week.

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.

Managing gray mold (Botrytis) on strawberries is increasingly challenging because of fungicide resistance development, plus a new Botrytis species that is less susceptible to fungicides is becoming common in the mid-Atlantic region. Resistance to certain fungicides is also a problem in management of anthracnose fruit rot. This article describes disease management strategies designed to slow further resistance development, while also providing specifics for managing our two most common fruit rots. Authors: Dr. Mengjun Hu, Univ. of Maryland, and Kathy Demchak, Penn State Extension

As you’re scouting fields this summer, keep this fungal disease in the back of your mind. Tar spot is a fungal disease of corn caused by Phyllachora maydis. It was first discovered in the United States in 2015. In Latin America where tar spot is more common, another fungal species, Monographella maydis, is known to occur in complex with P. maydis; however, only P. maydis has been found in the United States.

Agronomy News-October 2022, Volume 13, Issue 7. Topics in this issue are Survey of the Most Common and Troublesome Weeds, Farm Emergency Action Plan, Preparing for 2023: Small Grains Disease Management, Maryland Accepting Proposals for 2023 Animal Waste Technology Fund, Scouting For Ear and Stalk Rots in Corn, Keep An Eye On Nitrogen Fertilizer Prices, Grain Market Report, Weather Outlook, and Regional Crop Reports.

Distinct lesions patterns along leaf veins are signs of anthracnose disease on shade trees.