With the bitter taste left by head scab and high vomitoxin levels in this year’s wheat crop, many producers are wishing they would have sprayed fungicide this year. Those with whom I’ve spoken who applied a product were glad they had. So this brings up the discussion of when and what do I spray, and, beyond that, do I even need to spray? This is a very vague question and the answer really depends on the situation. The question I need to pose is will the economic loss imposed by the disease, insect or weed that is causing yield loss be greater than the cost of treatment? If so, then yes is the answer.
Far too often when producers hear of diseases in the state, knowing they have susceptible varieties will want their field sprayed. When dealing with crop disease, first you need to understand the disease and the conditions that cause it. Since head scab is such a big topic this year, let's use it as an example. Most of my information on this topic will come from the website: http://www.oardc.ohio-state.edu/ohiofieldcropdisease. This website details information on the most common and economically relevant diseases in Ohio for corn, soy and wheat.
Environment is the first factor to look at. When I speak of environment, I mean weather and field conditions. This year we received light rain and warm weather during most of the spring during and slightly after flowering in wheat. When dealing with a fungus, like Fusarium graminearum that causes head scab, warm, wet conditions are a red flag. But that is only one flag! Don’t spray based on that condition alone! Along with weather, field conditions play a role in the life cycle of Fusarium. Corn and wheat residues, along with rye, barley, oats and many weeds, like foxtail, can act as hosts for head scab, allowing it to survive into the following crop. No-till fields tend to have higher concentrations of residues on the surface, making them more susceptible to disease. So when we have warm, wet conditions during flowering, and high levels of residue on the soil surface, we’ve got a bigger red flag. But don’t spray just yet!
Is your variety of wheat susceptible or resistant to head scab? That is a great question for your seed dealer. There isn’t a variety of wheat that is completely resistant to head scab. If you poke around the website I listed above, or consult one of the OSU Extension publications on crop diseases, you will find that varieties are resistant in many ways. Some varieties mature earlier or later than others, possibly escaping the warm, wet weather during flowering. Other varieties seem to isolate the infection to just a few florets on the head. So if we have warm, wet weather conditions in the spring, with high levels of crop and weed residues on the soil surface, and a susceptible variety out there, we have a red flag.
O.k., spring time comes and we have met all of the qualifications above, is it time to spray yet? Well, maybe. Timing is very key to spraying. Spraying because the crop dusters are in the area this week, or you see a problem from the road, is not recommended. Weeds, diseases and even insects require proper timing of application for control. This can vary because of what product you are using, too. If you come to my presentation on August 3rd, at OSU Extension, Darke County, at 6:00pm, you will find out timing is everything, when it comes to controlling giant ragweed and marestail. Shameless plug behind me, let’s get back to head scab.
Application timing for head scab revolves around controlling the fungus early on and maintaining harvest requirements for the fungicides. You need to apply products for control at a point that maximizes efficacy and allows enough time to allow safe harvest. That time varies by fungicide, but for wheat fungicides it can be anywhere from 30 to 45 days. How do we know when the proper time to spray is? SCOUT!
Getting out into the fields soon after flowering and looking for diseased or dying heads is a key indicator of the need for spraying. Walking three rows in from the road and looking at a few heads is a terrible way to make a decision. Walking the whole field and taking random samples from at least five locations is recommended. In proper scouting, try to walk a zigzag or W pattern across the field. Vary your distances between samples points to make things more random. Don’t have time? Consider hiring a consultant who will come scout your fields for you. Like crop insurance, it’s a good thing to have.
Are you confused yet? If yes, then you are not alone. The decision of when and what to spray, or even if you need to spray, is a hard one that can vary from year to year. Controlling something like head scab is better fought with management. Rotate crops with two to three years between wheat. Try to plant wheat after soybeans. When purchasing your wheat, consider varieties with resistance to some major diseases. Plant varieties that will mature at different times, to limit exposing an entire crop to disease. Keep wheat away from corn and wheat residue. AND my favorite recommendation, control your weeds! This next recommendation may be a little taboo in these modern no-till times, but if we do have an outbreak of a disease like we did this year, consider tillage to bury the residue. When key points in pest life cycles come up (flowering in many cases), watch the weather and get out and scout!
Will doing all this ensure a pest free crop? Nope. Sometimes life gives you a pair of twos in a game of flushes and straights. Unfortunately you can’t bluff your way out of head scab. But, by managing your fields and keeping track of what the current conditions are, you can minimize your risk. If you have any questions or concerns about spraying, want to learn about scouting, or have any other questions, contact me, Justin Petrosino, at Ohio State University Extension, Darke County, at 937.548.5215. Please review the CORN newsletter at http://corn.osu.edu/ for updates on head scab and other crops news. Oh, and if you don’t have anything going on the evening of the 3rd, come learn about giant ragweed and marestail at OSU Extension, Darke County, at 6:00pm.
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* Darke County Extension
* Ohio State University Extension
* E-mail: dark@agvax2.ag.ohio-state.edu
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