Reports of late planting, flooding and saturated soils are inundating news sources right now, and corn growers need to take them seriously. All of these conditions will likely have an effect on which pests and diseases show up in your cornfields. Extension specialists advise keeping a close eye on crops as they emerge.
“Soggy soils certainly are favorable for important seed rots and seedling diseases of corn, especially Pythium diseases, which are very common in our soils,” says Paul Vincelli, University of Kentucky plant pathologist. “Common seed-treatment fungicides provide a fair amount of protection against seed and seedling diseases, but there is a limit to how much they can do, especially with the cool, soggy soil conditions prevailing at the moment. It’s always a good idea to monitor corn stands for emergence and stand establishment, but especially this year.
“Continued sogginess is also resulting in major delays in planting. Corn crops planted in early to mid-May and beyond are at greater risk from a variety of destructive diseases, especially gray leaf spot, northern leaf blight, and southern rust,” he adds.
Marcia McMullen, North Dakota State University Extension plant pathologist, echoes the Pythium concern.
“Pythium species are ‘water molds’ producing swimming spores in wet soils, spores that can infect corn roots. Pythium root rots are favored by high soil moisture levels and low soil temperatures. Most of the commercial seed sold, however, should be already treated with a fungicide seed treatment that contains fungicides that are active against Pythium,” she says.
“Later on, if excessive moisture continues, other problems may develop, but I think the seedling problems from root rot are primary now,” McMullen adds
According to North Dakota State University, today’s common small-grain fungicide seed treatment products provide protection against a number of disease organisms that could be favored by poor planting conditions and cause seedling blights or root rots. In addition, some products may also be combined with an insecticide to provide protection against insects, such as wireworm. NDSU recommends using a broad-spectrum fungicide product for good disease control; a producer needs to assess the risk of insect damage to make a decision on adding insecticide.
Ohio State Extension Entomologist Ron Hammond advises closely monitoring corn crops to prevent insect injury.
“As we get into early to mid-May without a lot of planting of either crop, my biggest concern is that many pests will be at a stage where they can cause significant injury just as the crops are emerging and are small in stature – i.e., not very big with little leaf area,” says Hammond.
“Cutworms will be getting into their main feeding stages; slugs will be getting large enough to cause significant injury; stalk borers will be larger, armyworms if around the same thing. Insect damage is often based on the insect-plant interaction, with the size of the plants being an important aspect of this relation. The larger the plant, the better off the grower might be with less economic damage occurring,” he says. “This year, it appears that much of the crop will be quite smaller than normal, with much just emerging. I think that the crops will need close monitoring to prevent significant injury from occurring because of the size of the crop.
“Whether the late plantings affect the timing of the growth stages later in the summer that relates to insect-host damage relationships remains to be seen, mainly because if changing to short season hybrids will affect things, and with soybeans, flowering stages are more affected by day length and will probably still occur at the normal time,” Hammond says.