Richard Taylor, Extension Agronomist; rtaylor@udel.edu
With corn harvest proceeding much earlier than in ‘normal’ years, many growers could be considering whether to go ahead and plant their wheat or barley crop in the next few weeks. The recommended or suggested planting date varies from county to county based on the Hessian fly-free date. (For more information on Hessian fly see the article by Joanne Whalen “Agronomic Crop Insects – September 7, 2012” in issue 20:25 of the Weekly Crop Update) The fly free dates are Oct. 3 for New Castle County, Oct. 8 for Kent County, and Oct. 10 for Sussex County.
For barley, we have conducted planting date studies in Sussex County comparing early-planted (September 26) barley with a close to suggested planting date (October 7). Our results indicated a fairly consistent 5 percent reduction in yield with September planted barley as compared with the October 7 planting date. Winter weather in the years the study was conducted did not result in significant visual winter injury to the barley so the impact appeared to be more of a general nature. Barley planting was dramatically affected by late planting unlike wheat. Delaying barley planting by just one week to October 15 resulted in a (four year average) yield reduction of over 15 percent and delaying two weeks to October 25 resulted in an over 20 percent yield reduction. Delaying planting barley until November increased the yield potential reduction to over 40 percent.
For winter wheat, experience has to be our guide with respect to planting date. We have evaluated the ideal planting date versus later planting dates but not against a September planting date for wheat. However, we can use both past experiences and basic agronomic knowledge to evaluate the risk involved with early planting wheat.
Since September planting dates are before the Hessian fly-free date for all our counties, we can surmise that the risk of lodging during grain fill will be increased versus planting after the fly-free date. You do need to keep in mind that the fly-free date is based on temperature averages and during warmer than normal falls fly emergence and egg-laying activity can extend past the listed dates. Larval activity can cause lodging, stunting, and yield loss since wheat tillers can be severely injured. In past variety trials, we have seen significant injury and yield reductions on susceptible varieties. Early planting of wheat can increase your risk of an infestation especially if wheat is planted in fields with wheat stubble or in fields next to one with wheat stubble.
For wheat that is planted following dryland corn, the greatest risk this year likely is due to excessive soil residual nitrogen (N); or, if the fall weather is warm and moist, to fall N mineralization from the high levels of nitrate in the dryland corn residue. High fall N availability can lead to excessive growth that will be more susceptible to winter kill or injury if we have a cold, open winter. In past years, we have had many growers asking what they could do about all the excessive top growth that occurs when wheat is planted in September and fertility levels are high. In some areas of the country, the extra foliage is used to graze cattle or sheep but most Delaware farmers do not have this option. The option tried has been to mow off and sometimes remove the excessive top growth. This has at least in part been successful in reducing winter injury but there are significant costs associated with the practice.
Another concern that again depends on fall weather conditions as well as insect populations and a residue of disease inoculum is the development in September planted wheat of disease or insect problems. In particular, barley yellow dwarf virus, which is transmitted in the fall by aphids feeding on the lush growth, can cause more severe injury than spring infections. The lush growth of early planted wheat could be more of an attractant for aphids but certainly will have a longer exposure to the risk of infestation.
All these cautions are not to say that you should never plant wheat or barley before the fly-free date only that you should be aware of the possible consequences and make a decision on when to plant and how many acres to plant from a position of knowledge.