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No-till notes "Wheat stem sawfly"

 


As I mentioned in a previous article I had a nice visit with Dr. Jeff Bradshaw about the wheat stem sawfly. Dr. Bradshaw has since sent me an article about the wheat stem sawfly and some management practices producers may want to consider for their own operations to begin combating the presence of this insect in their winter wheat production practices. The following is the article Dr. Bradshaw was kind enough to send to me.

“A NEW RESURGENCE OF AN OLD PEST OF WHEAT: WHEAT STEM SAWFLY

Jeff Bradshaw, UNL Assistant Professor and Extension Specialist

The wheat stem sawfly has been around for a long time. It was first detected in California in the 1800s and moved northward into British Columbia. Sometime during the early part of the 1900s the seasonal cycle of this insect reportedly began to emerge earlier to coincide with stem elongation of winter wheat. Ever since this shift, this insect began a steady march southward into the northern High Plains of the United States. The wheat stem sawfly was discovered by Gary Hein, UNL entomologist, in Nebraska in the mid 1990s. However, it hasn’t become a major issue until that past three years in the Central High Plains. There are multiple possible reasons for its recent expansion, such as our recent spell of relatively mild winters. However, this insect has adapted to survive winters in our environment in the residue that we leave behind in our wheat fields. Therefore, any activity that conserves wheat residue will likely conserve the overwintering habitat for the wheat stem sawfly. That is, the expansion of acres using some form of conservation tillage has likely contributed to the prevalence and spread of this insect.

Even though this insect has been around for a long time, there is still much that is not understood about this insect, particularly in our environment. Currently, through support of the UNL Agricultural Research Division and the Nebraska Wheat Board, my lab has just begun a project to understand some possible management options for this difficult pest. I hope to see two outcomes from our research. One is greater clarity on how specific crop rotations or, possibly, creative uses of trap crops might enable us to reduce regional levels of the wheat stem sawfly. The second, longer-term option, is to work with plant breeders to develop varieties that express increased level of natural, insect resistance compounds.

So what does this mean for Nebraska wheat growers? As many growers know, pest management can be a little bit like a game of Whack-a-Mole; one challenge down and another one pops into place. I would not recommend that we go back to mold-board plowing for managing this pest. In most cases there are too many economic and environmental advantages to conserving some residue to make conventional tillage systems a level-headed option in this case. That is why I am currently conducting the research above; to improve our tool chest for the long term. What is needed now are options that keep us advancing forward as an industry. Below are some options that growers might consider in managing this insect pest in the short term. These may not be good options for every grower, but perhaps some are worth considering. It is important to remember that all of these management options only manage wheat loss from lodging, the stem-feeding behavior of the stem sawfly can reduce yield as much as 15% just from feeding without lodging.

SHORT-TERM OPTIONS FOR WHEAT STEM SAWFLY MANAGEMENT

Do nothing. If you do not have a history of lodging at your location, you may not need to take any action. Or if the area that is infested is minimal or your yield expectations are low in the affected area, you may not want to consider any action.

Swath harvest. Swathing equipment might be hard to come by, but you could swath and wind-row your wheat while it is still somewhat green at the end of June. Doing so would cut the wheat before the sawfly has a chance to cut it

Get low. Harvest at a normal time with a low-cutting, floating-head combine. However, this harvesting method may not be compatible with some residue-management operations.

Plant a hard-stem variety. Some have considered this option for their 2013 planting. These varieties will yield less than hollow-stem varieties, but the hard stems are resistant to lodging. Also, there is some thought that stem sawflies can not complete development in hard-stemmed varieties. Therefore, some growers have considered planting boarders of hard-stem wheat to try to trap the sawflies. However, an effective trap-crop size has not been determined.

Crop rotation. There are a number of crops that are not hosts for the wheat stem sawfly. The stem sawfly only attacks grasses such as wheat, barley, wild rye and other native grasses. Within crops, the wheat stem sawfly predominately damages wheat and some varieties of rye, barley and oat (although larvae are not known to survive in oats).”

I want to thank Dr. Bradshaw for sharing his ideas with us on managing the wheat stem sawfly. For my own operation I think crop rotation has already shown merit as we haven’t noticed a real problem with this insect in our own fields. Each producer of winter wheat will have to decide a management practice which will help control this problematic insect until other viable alternatives are discovered through research. 

 

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