PPFS-AG-SG-6



<H1<CENTER><H1>PREPLANT DECISIONS GREATLY IMPACT DISEASE POTENTIAL IN WHEAT</H1></CENTER></H1><BR>




	<H3>Donald E. Hershman</H3>					(Revised 7-94)<BR>




A large number of Kentucky wheat producers have their total disease management program in place once the seed is in the ground.  By that time decisions have been made relative to crop rotation, tillage/seed bed preparation, variety selection, seed quality, seed treatment, planting date, seeding method, seeding rate and fertility.  Individually and collectively, all of these decisions can play an important role in influencing which diseases develop, their severity, and their ultimate effect on yield/test weight - the producer's bottom line.  Because pre-plant and planting decisions are so important in the management of wheat diseases, you need to understand how they affect disease.<BR>




<B>VARIETY SELECTION</B><BR>


	Decisions relating to variety selection are, perhaps, the most important decisions one can make in managing diseases.  All commercially available wheat varieties have a unique spectrum of susceptibilities to diseases common in Kentucky.  Which and how many varieties are planted predetermines the potential for certain diseases to become a problem, as well as the severity of those diseases given the proper environmental conditions.  Failure to consider the ramifications of variety selection in managing diseases is a costly mistake made by many wheat producers each year.  Select two or three varieties with the greatest amount of available resistance to the diseases most common on your farm and in your community.  This requires you to have some idea about the disease history on your farm.  If you don't have this information, talk with your ag agent, your farm supply dealer and/or your neighbors.  This information won't be as good as actual data from your farm, but it will be far better than basing decisions on no information.  It is important to plant more than one variety for one key reason: it is very common for a single disease to severely damage a single variety.  This is less likely to occur when multiple varieties are planted.  Hence, your risk level is reduced.  Planting more than one variety, especially when different maturities are represented, can also help with the logistics of harvest and soybean planting.  For more information on disease reactions of commonly grown wheat varieties, consult the Kentucky Small Grain Variety Trials Report available at your county extension office.<BR>







	

<B>CROP ROTATION</B><BR>


	Crop rotation helps in the management of wheat pathogens that survive between wheat crops in the residue of a previously diseased crop.  When a non-host for a pathogen is grown in a field, the levels of that pathogen will decline as the residue from the previous wheat crop deteriorates.  This can translate into reduced disease pressure the next time wheat is produced.  Rotation is helpful in the management of "hidden" diseases such as Pythium root rot and very destructive diseases such as take-all.  In fact, rotation of fields out of wheat or barley is the only practical means of controlling take-all.  Rotation can also reduce infections by the tan spot fungus and Septoria.  However, the effect of rotation on these diseases can be negated by spores blowing into fields from neighboring fields.  Most wheat in Kentucky is planted following corn.  Corn is, generally, a good non-host crop to grow in non-wheat years.  There has been some talk that planting wheat behind corn increases the chances for a head scab problem in wheat.  The reason is that the head scab fungus can also attack corn and result in stalk and ear rots.  The experience of most producers is that planting wheat behind corn does not increase the amount of head scab in wheat.  The reason is that there is so much head scab inoculum blowing around that the disease will be a problem regardless of the rotation as long as conditions are favorable for head scab development.<BR>




<B>TILLAGE</B><BR>


	Tillage of wheat stubble hastens the breakdown of residue that harbors certain disease organisms.  This can help reduce levels of take-all and foliar diseases such Septoria leaf blotch and tan spot.  "Help" is the operative word here, since it is unlikely that tillage will be of much good in the absence of other control methods.  For fields in wheat/soybean - corn rotation, tillage prior to planting corn should be sufficient to cause a significant decline in surviving wheat stubble.  The year between wheat crops in this rotation will also help, except where high levels of the take-all fungus exist.  In those cases two or more years between wheat crops may be required.

	Planting wheat no-till following corn will not be a problem with one possible exception.  That being where Gibberella stalk/ear rot was a problem in the corn.  This same fungus causes head scab in wheat. Generally no-till wheat behind corn does not result in significantly greater problems with head scab compared to where corn stubble was tilled.  Nonetheless, this practice may increase the risk for head scab to develop in wheat in some cases.<BR>




<B>SEED QUALITY, SEED FUNGICIDES, SEEDING RATE, AND PLANTING METHOD</B><BR>


	All of these can affect stand establishment and development.  To achieve the highest possible yields, you must have sufficient stands.  To achieve the desired stands, you must have excellent seed germination and development of seedlings.  Using high quality seed that is treated with a broad spectrum fungicide and good 


planting techniques will foster good stand establishment.  Excess stands, however, will encourage foliar and head diseases by reducing air circulation and light penetration into the canopy later in the season.  Use your experience and calibrate your equipment to achieve sufficient, but not excessive, stands.  Ask your county extension agent for more information on planter calibration and proper seeding rates and methods.<BR>




<B>PLANTING DATE
</B><BR>

	Producers are tending towards planting wheat earlier and earlier each year.  Early planted wheat is wheat planted prior to the Hessian fly-free date is at greater risk of damage caused by barley yellow dwarf, take-all disease, and Hessian fly than is later-planted wheat.  If logistical considerations cause you to plant some of your wheat acres prior to the fly-free date for your area, make sure those acres have been well-rotated and plant a variety that can tolerate some barley yellow dwarf.  Planting all your wheat acreage prior to the fly-free date is extremely risky.<BR>




<B>FERTILITY</B><BR>


	Too much nitrogen in the fall can encourage excessive fall growth that can increase your problems with barley yellow dwarf and most foliar diseased caused by fungi.  Increased problems with yellow dwarf has to do with an extended period of aphid activity (aphids transmit barley yellow dwarf) when stands are dense in the fall.  The same situation encourages infection and overwintering of foliar diseases such as leaf rust, powdery mildew, and Septoria leaf blotch.  Excessive spring nitrogen results in lush stands that promote disease in a manner similar to that associated with excessive seeding rates.