ATLANTA, Ind. — In many ventures, timing and attention to detail is everything.

This is especially true in farming, with current low commodity prices creating a tighter bottom line.

One of farmers’ primary concerns especially with recent rainy weather is crop disease. A wet spring followed by cold temperatures in much of the Midwest brought about excellent conditions for fungus. This is where scouting and proper fungicide decisions are important, said Chad Kahler, in a recent Beck’s Hybrids webinar aimed at producers.

“(If you spray), wait until disease lesions add up to about the size of a quarter.

That’s the point when I start to get concerned about pulling the trigger on a fungicide application,” he said.

Scouting times are important. “The sweet spot of scouting (in corn) is the tassel emergence and ear emergence stages. When you see the ear leaf coming out, that is the time you need to scout for diseases. The first phase of scouting I would recommend for soybeans is generally R-1 through R-4, beginning flower through full pod.”

The principal diseases that might justify a fungicide treatment in most Midwest cornfields are gray leaf spot and northern leaf blight. Soybean diseases that might warrant a fungicide application include anthracnose, brown spot, cercospora leaf blight, frogeye leaf spot, pod and stem blight and soybean rust.

“Finding diseases in corn early is important,” said Kiersten Wise, plant pathology extension associate professor at the University of Kentucky College of Agriculture, Food and Environment. “The best time is at tassel; this way you can get a fungicide plan in place and send any possibly diseased samples to get tested.

“In corn, grey leaf spot and northern corn leaf blight tend to top the list of diseases that we are looking for; common and southern rust are the others.”

Wise stressed the importance of checking proper areas of the plant. “It is important to look at the entire part of the plant. In corn, make sure you check above and below the ear leaf. Most diseases will progress from the bottom to the top, but don’t forget about checking above the ear.”

“We really want to focus most of our attention on looking at the middle of the canopy and above,” said Kahler.

“There are some exceptions to this, though. We don’t need to disregard the lower canopy. Sometimes white mold and septoria brown spot will appear at the bottom.

“Usually by the time we get to the R-3 growth stage, I’m looking for septoria brown spot, which may have moved to the middle of the canopy. If it makes it to the middle of the canopy, I would recommend a fungicide at that point.”

Types, uses of chemicals

There are three main classes of chemistry to which a fungicide will belong, said Kahler. “The first one is triazole. That is more of a curative type of fungicide, it will help cure the spread of the disease. I don’t really like to use that term because it’s not curing the disease itself.

“The next class would be the strobilurins. Those will be preventative. You would want to use those on the early side of the application window. The third class of chemistry is the carboxamide class. This is also a preventative class.

“I recommend combination fungicides, and now we are beginning to see the emergence of three-way fungicides with all three of these classes in one product,” he noted.

Volatile weather in some parts of the country has caused enough stress on crops this year to make them more susceptible to fungal disease. Luckily, theMidwest has not seen much in the way of disease activity, said Kahler. “Southern rust this year is only reaching as far north as Arkansas and Tennessee. I’ve not seen any confirmations in Illinois. In Tennessee; that’s very limited.”

Concerns about fungal disease have caused a dramatic expansion of foliar fungicides in the past decade. Once reserved for seed production fields, for seed quality protection in specific circumstances, applications have moved toward an increased use of fungicides as a means of maximizing yields.

Several factors have come into play to cause this, including the development of strobilurins, broad-spectrum fungicides registered for the control of foliar diseases of a number of crops, including soybeans and corn. Additionally, soybean rust concerns and subsequent educational programs led to a greater awareness of fungicides.

If fungicides are needed, there is only a short window when chemicals can be used. Fungi have certain life stages that are vulnerable to fungicides, and plants have vulnerable stages which would require protection when the risk of the target disease is high. If chemicals are applied outside that window, it might not produce the desired results.

If applied prematurely, fungicides will lose their effectiveness by the time the disease makes its appearance – generally 21 days.

“Applying fungicide (in corn) pre-tassel is not something I’d recommend,” Kahler explained. “I’d recommend you wait until the entire field is just tasseled. This year it’s a hard decision because we have areas that will be tasseled a lot quicker than other areas in the field.

“What many people tend to forget about is late-planted corn is (it is) more susceptible to disease than early-planted corn in most cases because if we do have late-planted corn, it’s going to be at an earlier growth stage once the disease sets in. It’s going to have more time to cause yield loss.

“When we look at all of our data and all of our timings (for soybeans), R3 tends to be the sweet spot. It takes the least amount of price per bushel to be able to break even on that application at R3. Timing is pretty critical,” he said.

“R2 and R4 look like they tend to take more per bushel with fungicide and insecticide applications, but this data can be misleading. It really depends on the environmental conditions that you have at full flower to full pod stage. There is really a 20- to 30-day window between R2 and R4.”

For information regarding pesticide use in their specific region, farmers need to contact their local extension agent.