September 17, 2003

Fall is the best time to identify and control ryegrass and cheat. If you have had a problem in the past or want to avoid a potential problem, fall is a good time to take action. Plus, fall grass is smaller and usually requires less product to provide control.

Ryegrass has a “diesel-wash” appearance from a distance, and, in general, is a smooth plant (no hair). Hoelon (diclofop) and Achieve (tralkoxydim) are labeled for ryegrass control. Ryegrass resistant to Hoelon and Achieve has been identified in Arkansas, so be on the look out for any unexplained control failures. One herbicide alternative for resistant ryegrass is Finesse. Finesse has not been tested in wheat weed trials at the Delta Center so specific information is unavailable. However, Finesse’s supplemental label indicates that the crop rotation interval is 6 months after the last application and to plant only STS soybeans in order to avoid injury. Read the label carefully for all of these products.

Unlike ryegrass, cheat, in general, is hairy. Sencor (metribuzin) is labeled for tolerant wheat varieties but must be timed properly. A fall application of 2 to 3 ounces of Sencor per acre will provide some control of young cheat with a reduced chance of injury to wheat. Apply Sencor to 1 to 3 inch cheat and after wheat plants have 2 leaves and 1 inch secondary roots. Another option labeled for wheat to control cheat is Maverick. Monsanto’s Maverick has not been tested in wheat weed trials at the Delta Center so data is unavailable. Maverick’s label indicates that in order to double crop you must use STS soybeans, the soil pH should be less than 6.5 with accumulated precipitation of 30 inches and a rotation interval of 3 months is necessary. Finesse has a supplemental label primarily as a tank mix partner with Sencor.

The key to preventing these weeds from becoming a problem in the spring is to start scouting shortly after wheat emergence and applying the necessary product in the fall. As always, with any product read the label carefully.

Wheat production information is available on the web at http://www.psu.missouri.edu/cropsys/Wheat/. This web page contains variety performance testing from several Universities along with general production information. The 2003 University of Missouri Crop Performance books finally arrived in the office. When selecting a variety consider yield potential, test weight, disease and insect package, heading date and maturity date.

Consider the quality of the wheat seed you select. If you plan to use saved seed be sure it is properly cleaned. Cleaning the seed will remove small and/or shrunken kernels, which may be infected by seed-borne pathogens. You may also want to consider a fungicide seed treatment. It is also recommended to have a germination test done. Knowing the germination rate will allow for accurate seeding rates. Typically, wheat with a germination below 80% should be avoided. Seed quality also includes seed size based on a thousand kernel weight (TKW). If possible select a seed with a TKW of 30 grams or higher, because these seeds tend to have increased fall tiller number and seedling vigor.

Wheat does not tolerate wet feet, therefore select well drained fields and improve drainage in wet spots. Applying 15-25 lbs of nitrogen along with P and K following corn, grain sorghum or rice can improve crop health and root system. Phosphorus is essential for good fall and early spring growth. Target P level for wheat is 45 lb P/Acre. If unsure of your soil nutrient levels consider having your soil tested.

The optimum planting date can be a challenge and it is dictated by weather and harvest of the previous crop. With this in mind, The University of Kentucky recommends a planting date period of October 10 through October 30 for Kentucky.

The University of Missouri’s optimal planting date is based on Hessian fly free date which is October 14. Wheat planted prior to this date is at an increased risk of yield loss associated with Hessian fly, aphid feeding, Barley Yellow Dwarf virus as well as excessive fall growth which increases the risk of spring freeze injury. Another date to consider is the average first frost which for Scott County is approximately October 30. Although wheat will germinate in soil temperatures as low as 40 degrees, planting later than November 1 increases the risk of poor fall tiller development, winter injury, and heaving.

An optimal final fall stand should be approximately 35 plants per square foot. To obtain an optimal stand, base seeding rate on seeds per acre and it should be between 1,300,000 to 1,500,000 million seeds per acre. Ideal seed placement is between 1 and 1.5 inches deep when soil moisture is adequate.

In the fall, the primary concern is aphid management. There are four species of aphid that could potentially attack wheat. These include the greenbug, English grain aphid, Bird cherry-oat aphid and the corn leaf aphid.

The greenbug can be a serious pest in wheat because of the toxic saliva it injects into the plant producing yellow leaves and chlorotic spots. The greenbug can be identified by it’s pale yellow body and dark stripe down the back. Missouri and Arkansas have set the threshold for greenbug aphids at 50 aphids per linear foot of row. Kentucky’s action threshold is 10 aphids per foot of row in the fall.

The biggest threat that English grain and bird cherry-oat aphids pose in the fall is the transmission of Barley Yellow Dwarf Virus (BYDV). However, controlling aphids at threshold levels is only a small part in reducing the risk of potential BYDV infection. Management also should include destroying any volunteer wheat or grass weeds in the field, avoiding an early planting date in order to minimize the window that insect vectors can transmit viruses to young plants, and maintaining good plant vigor. English grain aphids are pale green with long black antennae and cornicles. Bird cherry-oat aphids have a mottled, yellowish to olive green to black coloration with black antennae and legs plus a red patch at the base of the cornicles. Missouri’s and Arkansas’ approach to BYDV management focuses more on timely planting to reduce the amount of time for aphid populations to build up in the fall. Kentucky takes a more aggressive approach to aphid management when BYDV is a concern. Kentucky’s viral thresholds are based on crop age: 30 Days after emergence = 3 aphids/ row foot; 31-60 Days = 6 Aphids; and 60 + days = 10 Aphids. Insecticides that can be used are Warrior, Di-Syston, Dimethoate, and Lannate.

When scouting your wheat keep in mind to evaluate the entire field and not just the spot closest to the field road. Aphid populations will generally be highest close to the edges, so making a decision to treat based on one location may not be the most economical.

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