Weed Control Requires Fine-Tuned Approach

 JACKSON, TENN.
   Seven or eight years ago the main weed call in wheat was Italian ryegrass. That has changed over the last several years with henbit and poa (annual bluegrass) causing the most problems in wheat. Some have asked if Harmony will provide any control of these two weeds. Harmony at best will only provide about 60 percent henbit control and will be no help on poa. The best herbicide option is metribuzin. In our research 4 to 5 ozs/A of metribuzin (Sencor) will provide at least 80 percent control of henbit and over 90 percent control of poa.
   Of course the concern with metribuzin is that some wheat varieties vary on their inherent tolerance to this herbicide. There are wheat varieties listed on the metribuzin label that have good tolerance. Unfortunately, those varieties are ancient history. Three years ago Bob Scott and I screened pretty much all the commercial varieties grown in the mid-south for metribuzin tolerance. This data can be accessed online at: (http://www.utcrops.com/wheat/wheat_pdf/S encor%20Word%20copy.pdf). Most varieties had good tolerance. However, in just 3 years there has been almost complete turnover of wheat varieties grown in the mid-south. None of these new varieties have been formally screened. The question I have been asked often this winter is x, y or z variety sensitive to metribuzin? I have no data on these new varieties so their guess is as good as mine. What I can say is that metribuzin has been used widely on wheat in Tennessee this past fall and early spring with no reports of any variety sensitivity. Metribuzin can be applied to wheat up to the jointing stage.
   There have been a few calls coming in with folks interested in spraying wild garlic (onions) in wheat. The main concern is whether or not there is enough new growth on the wild garlic to obtain good control with Harmony Extra. Harmony Extra is primarily taken up through the foliage. Therefore new growth in the spring is essential to obtain good control. The Harmony Extra label states that 2 to 4 inches of new growth from stressed weeds is essential for good control. The mistake many make is to look for the new growth at the end of the garlic leaf. The new growth actually comes from the bulb area and not from the end of the leaf. Some have also asked about adding Clarity at this time with their Harmony Extra. Clarity can be safely used in wheat up to the first wheat joint. Though I haven’t seen every field, it is apparent there is little garlic pressure in the wheat sowed in fields that have been in cotton for several years. In a few fields there has been so little it was not worth spraying. It may save you some money to step out and scout the garlic level in some of these fields. Δ
DR. LARRY STECKEL: Extension Weed Specialist, University of Tennessee