Drought: Implications for near-term management decisions in field crops

The recent trend in higher than normal temperatures paired with lower than normal precipitation puts Michigan field crops at risk.

Below are some considerations raised by Michigan State University Extension educators and specialists that growers may want to consider implementing if drought conditions continue or intensify.

Prevent fires during wheat harvest

Many wheat fields yet to be harvested may have particularly dry chaff and straw during the weeks to come. Exhaust pipes, worn bearings and broken, internal equipment parts can readily ignite the flammable chaff and straw that inevitably collects within the combine. Growers are reminded to make sure that combines are clean and in good working order; remove collected chaff after every couple hours of operation and check to insure that the combine’s fire extinguisher is in working order. Operators might also consider having a shuttle of water at hand to immediately respond to an equipment or field fire. (Martin Nagelkirk, MSU Extension Educator)

Manage potato leafhoppers in alfalfa and dry beans

Potato leafhoppers are “thick” this season in fields and roadside vegetation. As ditch banks and roadsides dry down, these leafhoppers will move into fields. Leafhoppers in alfalfa will also move into neighboring fields after cutting. Thresholds for alfalfa are based on a combination of numbers of potato leafhoppers per 100 sweeps and plant height (3 inches = 20 potato leafhoppers; 3 to 8 inches = 50 potato leafhoppers; 8 to 12 inches = 100 potato leafhoppers; over 12 inches = 200 potato leafhoppers). In dry beans, the threshold is only one potato leafhopper per trifoliate. 

Watch for spider mites in soybeans

During droughty seasons, spider mites become a concern in soybeans. Spider mites are often found along field edges and in dry spots in the field. You will first notice a yellowing of the leaves, but in severe infestation, whole leaves turn brown and eventually drop off. It is recommended to scout and spray only when mites reach a threshold to avoid rebounding of the populations. 

Scout irrigated fields for western bean cutworms

Western bean cutworms can overcome a lack of water if they find irrigated fields in the neighborhood. Under dry conditions, moths are attracted to these fields and egglaying may be heavy. Pay particular attention to irrigated fields for western bean cutworm scouting in July. 

Fungicides: To spray or not to spray?

Most foliar diseases are favored by rainy or humid weather conditions. We have seen very little foliar diseases in corn or soybeans with the warm and dry conditions that we have been experiencing. The greatest chance of returning a profit on a fungicide application occurs when conditions favoring disease are present and when disease develops. The decision to spray should be based on the presence of disease risk factors, such as the susceptibility of a hybrid or variety, previous crop, field history and weather.

In general, a susceptible corn hybrid or soybean variety is more likely to have a greater response to a foliar fungicide than a resistant hybrid or variety. Cropping history will have influence on disease as many foliar pathogens survive on residue, i.e., corn after corn or soybeans after soybeans promote disease. The disease history of a field should also be taken into account; fields with a disease history should be monitored carefully so that the best decision can be made. And, finally, the weather; the hot and dry conditions that we have been experiencing so far have not been favorable for most foliar diseases. If you do decide to spray, consider leaving replicated, non-treated test strips in the field to determine if you are getting a benefit.

For additional information, see Foliar fungicides for corn: targeting disease. (Martin Chilvers, MSU Department of Plant, Soil and Microbial Sciences)

Harvest alfalfa early or not at all

Drought-stressed alfalfa typically flowers earlier and at a shorter height than well-watered alfalfa. Harvest timing decisions during drought should be based on plant maturity stage, height and yield estimate. Harvesting at less than 28-day intervals should not harm alfalfa persistence as long as stems are more than 10 inches tall and flowering. However, such stands may not yield enough hay to cover the cost of harvesting. In that case, it will be more profitable to wait for rain and stand recovery before harvesting combined old and new growth. Remember that this material will be lower in forage quality than an ordinary cutting because of the old stems included. (Kim Cassida, MSU Forage Extension Specialist)

Get to the root of soybean problems

Drought symptoms usually occur in localized areas within fields and the severity of the symptoms also varies between the affected areas. There are two conditions that explain the spotty occurrence and severity of drought symptoms:

  1. Variations in the capacity of the soils to hold water.
  2. Variations in the plant’s ability to utilize the available water.

Factors that affect water holding capacity include soil type, topography, residue cover, tile drainage and compaction. Factors that affect the plant’s ability to utilize soil water are soil compaction, weed competition, nutrient availability, soil pH, soybean cyst nematodes, diseases and insects. Because many of these factors can be managed, producers should investigate areas exhibiting the most severe drought symptoms to determine the specific cause. In some cases, the soil type simply has a lower moisture holding capacity. However, in other locations, factors that can be managed such as soil compaction, soil fertility or crop pests may be exacerbating the drought symptoms. (Mike Staton, MSU Extension Educator)

When is supplemental nitrogen recommended for soybeans?

Numerous university research trials have shown that nitrogen fertilizer applications to soybeans are not profitable. This is because soybeans are able to obtain up to 75 percent of their nitrogen from bacterial colonies (nodules) living on their roots. However, if the nodules are not present in sufficient numbers, a supplemental nitrogen fertilizer application will produce an economic return.

Recommendations for assessing soybean nodulation and applying supplemental nitrogen fertilizer are available in the MSU Extension News article Evaluating soybean nodulation. (Mike Staton, MSU Extension Educator)

Forego foliar feeding until moisture returns

Drought stress much earlier in the growing season than what is typically expected for Michigan may have resulted in stunted plants with compromised root systems and, therefore, growers are considering foliar fertilizer applications. Regardless of application method, nutrient uptake, availability and transport are severely limited without sufficient water. Under high temperature stress and dry soil conditions, plants attempt to conserve water by closing stomata, which are microscopic pores or holes in the leaf and stem surfaces of plants used for gas exchange. Water soluble fertilizers applied as foliar sprays are intended to be applied to the leaf surface with nutrient uptake occurring through these open leaf stomata. Under the hot, dry weather conditions that much of Michigan is encountering, foliar nutrient applications will be mostly ineffective as plants close their stomata to conserve what little moisture may still be available.

If soil moisture conditions reverse and become favorable for plant growth, the use of mid-season foliar nutrient applications may be beneficial. However, foliar feeding of macronutrients (e.g., N, P, K) is difficult due to the large quantities required by the plant and may only benefit if the nutrient of interest is deficient. Foliar feeding macronutrients generally show no benefit if already present in sufficient quantities. Micronutrient (e.g., Mn, B, Zn) foliar feeds can be beneficial due to the small quantities required by the plant, but be sure that the nutrient is truly deficient before applying. (Kurt Steinke, MSU Department of Plant, Soil and Microbial Sciences)

Controlling tough weeds in tough conditions

In dry conditions, weeds tend to “harden off,” making herbicide absorption by weeds more difficult. This can make weed control much more challenging, especially with herbicides like glyphosate. To control some of these tougher to control weeds in Roundup Ready crops, increasing the rate of glyphosate to 1.13 or 1.5 lb a.e./A and including ammonium sulfate (AMS) at a rate of 17 pounds of AMS per 100 gallons can improve weed control successes. If using other herbicides that tend to cause herbicide injury (e.g., Cobra, Cadet, Raptor, etc.), consider spraying in parts of the day when temperatures are cooler to decrease chances of extreme herbicide injury.

Ultimately, weeds are more difficult to control in hot dry conditions, but best control is achieved when weeds are smaller, so don’t put off herbicide applications. Scout each field after application to determine control and if additional applications are needed. (Christy Sprague, MSU Department of Plant, Soil and Microbial Sciences)

Stay hydrated and know the signs of heat stroke

Hot weather can increase workers risk of heat stroke. To decrease your risk, drink plenty of cool, rehydrating drinks, wear temperature-appropriate clothing and avoid areas where temperature can rise quickly, like parked cars. Heat stroke is serious, so recognize the signs – high temperature, no sweating, headache and nausea, rapid breathing and pulse, confusion and passing out. Seek medical attention immediately if you or a co-worker exhibits these symptoms. For additional information, see Recognize the signs of heat stroke before it’s too late and Tips to stay safe in the heat. (Kelly Ewalt, MSU Extension Educator)

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