Attack on Plant Health

February 8, 2011 05:54 AM
Attack on Plant Health

Boosting wheat yields and profits is similar to entering the Kentucky Derby. If you’re going to stand a chance at winning the race, you better set yourself up for success, with a well-tuned combination of horse and rider. Wheat management is similar in principle: Growers need to begin with a sound fertility program coupled with quality certified wheat varieties proven to perform with their soils and management system. Seed should be planted to a uniform depth, evenly down the row and all across the field, preferably with narrow rows to create high yield potential from the very start.

Once the yield potential is created, fields should be scouted regularly to protect the yield potential. Regular field scouting is essential to monitor weeds, insects and diseases and their effect on plant health.

Weeds. Some producers don’t see weeds in their fields until they are visible from the road at 60 mph; then they decide to treat them. Such an approach is similar to the horse falling over as it leaves the starting gate. In replicated research trials, I have seen 5 bu. per acre yield increases from a fall-applied herbicide compared with an early spring treatment using the same herbicide and weed population.

Scouting for weeds early in the season is important in determining weed types and thresholds. Treating threshold levels of weeds in the fall before they compete with the crop, just as growers have been trained to do in corn and soybean fields, is key to high yields. In most situations, the cost of the herbicide is actually less when applying it earlier to smaller weeds, so the real decision is timing of application.

If you are working with a no-till system, scout fields well before seeding and determine if there is a sufficient amount of weeds to merit spraying a burndown product. Most fields do require a burndown treatment for volunteers, grass weeds or broadleaf weeds, but it depends on the
region and rainfall. Burndown applications obviously remove weed pressure, but they also help control the green bridge that provides the necessary host for numerous insects, including aphids.

Insects. Region and moisture levels influence insect types, levels and thresholds. The insect pests that impact wheat yields and quality most frequently are aphids, cereal leaf beetles and armyworms.

Aphids are by far the most common wheat insect pests. They can feed on the crop, and most types of aphids can vector a virus called barley yellow dwarf virus, which is transmitted to the crop while aphids are feeding. Symptoms of this are yellow, sometimes red, leaves coupled with stunted plants and reduced grain numbers.

Even relatively low aphid populations (especially during the fall and early spring) can have a big impact on yield. Regular scouting is essential to monitoring populations and deploying control measures if threshold levels are reached.

A well-timed foliar insecticide is effective in controlling aphids. Seed treatment insecticides should also be considered, especially when planting wheat early. Early planting usually increases the risk of aphid pressure and requires lower seeding rates, so costs per acre of seed and seed treatment insecticide are frequently lower.

Diseases. Many producers struggle to find time to scout their fields, especially later in the spring, when foliar diseases can quickly take a big toll on yields and quality. The later stages of wheat development frequently coincide with planting corn or soybeans across the eastern, southern and central U.S., and farmers usually focus on getting those crops in the ground, rather than scouting wheat for disease.

Depending on the variety, region and rainfall, at least five major diseases can impact wheat. Tan spot, mildew, leaf rust, Septoria nodorum (glume blotch) and fusarium head scab are the most common, especially in denser canopies. No-till wheat, especially back into wheat stubble (more common in the Central and Northern Plains), can provide extreme pressures of early season tan spot and mildew, so early scouting for these diseases and a proactive program of controlling them early with a foliar fungicide around fourth to fifth leaf stage is usually cost-effective, especially when followed up with a second application around flag leaf emergence to early heading.

The higher-moisture eastern U.S. region generally sees more pressure from later-season Septoria, leaf rust and fusarium head scab, so while early fungicides are a good investment, the well-timed later-season fungicides frequently pay bigger dividends.

Field scouting is not an expense; it’s a necessary investment. Many producers don’t rank scouting fields high enough on the list of priorities. If you can’t scout fields regularly, find someone trained with wheat management to help. Don’t second-guess a well-trained wheat agronomist—many of them have seen and experienced the impact of most weeds, insects and diseases, so if they say "spray," you better be turning the key in the sprayer!

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