Bob Mulrooney, Extension Plant Pathologist; bobmul@udel.edu
Soybeans
Now is the time to start checking soybeans for soybean cyst nematode. Once soybeans have reached the 3rd trifoliate leave stage (roughly about 28-32 days from planting) the white or yellow female cysts can be seen on the roots. If you see irregular patches of stunted soybeans don’t presume the stunting is from drought. Digging the plants carefully may reveal SCN is present and could be the cause of the stunting. If you are seeing many cysts and stunting on resistant soybeans it is time to rotate out of that field to reduce SCN egg numbers.
White and yellow female soybean cyst nematodes on roots, 34 days after planting
Corn
Three corn samples arrived in the plant clinic this week with bacterial stalk rot. If you are irrigating from surface water sources, such as ponds or ditches, there is a risk of bacterial stalk rot. The bacterial can be in the irrigation water and get trapped in the whorl, the ear leaf sheath, and the ear shank. These places provide a place for water to sit and the bacteria can enter the stalks and cause a soft decay of leaf sheath, stalk, and ear shanks. It is foul smelling as well. It appears as random infected plants in the field and as a result it does not cause major losses. Corn is thought to be susceptible for a short period of time and the older the corn the less likely infection will occur. There is no chemical control for bacterial stalk rot. Treating irrigation water in the system with hypochlorite is an alternative solution.
Bacterial stalk rot