Start In Now For Italian Ryegrass Control
DR. BOB SCOTT
JACKSON, TENNESSEE
Italian or annual ryegrass is a cool season annual grass weed. Over the past few years our ryegrass populations in Arkansas have become more resistant to numerous herbicides and herbicide families or modes of action. This began in wheat production with resistance to the accase inhibitors like Hoelon® and into the ALS inhibitors, such as, Finesse® and PowerFlex®. Today we also have ryegrass that is resistant to glyphosate and Select® when used for burndown applications ahead of planting in the spring. There are also reports of “reduced sensitivity” to paraquat. Spring burndown applications become more difficult for any herbicide program as ryegrass tillers and gets bigger often exaggerating the problem. This problem has progressed from south Arkansas to the north over the years and in many areas we have it as bad as our neighbors in Mississippi.
Currently, our research is focused on making fall residual treatments to fields for ryegrass control. These applications should be made in early fall prior to ryegrass germination. If ryegrass has already emerged it should be controlled by either adding a POST application of Select® or paraquat or preferably with tillage. Growers have reported success with planting a cover crop for the suppression of ryegrass in the fall as well. Command®, Dual®, Prowl®/trifluralin, Zidua® and Boundry® have all shown acceptable activity on ryegrass in the fall when activating rainfall is received. Tank mixtures with Valor® improve fall residual control. Be aware of plant back restrictions (MP519). Our basic recommendation is after October 1 in the south and after October 15th in the northern part of the state, preferably ahead of a rain.
Fall treatments also take advantage of the biology of annual ryegrass seed. Most ryegrass germinates in the fall once soil temperature drops and moisture is present. Studies have shown that around 95% of ryegrass seed germinates in the fall and winter months of the year its produced. In other words, if you can control the first flush it usually takes care of the problem or at least makes it much more manageable in the spring. In addition, one year of maintaining a field free of ryegrass can significantly reduce the soil seedbank of ryegrass seed.
If applications are to be deferred to the spring care should be taken to make burndown applications early. Select® is a good option where no resistance has been confirmed. Be aware of plant back restrictions. Paraquat (Gramoxone® and others) should be tank mixed with a photosystem II (PSII) inhibitor labeled for the crop that is to be planted. These tank mixes will improve control over paraquat alone. For example, in soybean paraquat plus metribuzin (a PSII), in corn you could use atrazine or metribuzin, in cotton you could tank mix paraquat with cotoran. There is not an effective PSII labeled for rice.
For rice, sequential applications of paraquat may be required for acceptable ryegrass control. Although ryegrass has not typically been a problem long term in rice due to the establishment of a permanent flood. In can interfere with planting and early growth of young rice, infest levees and field margins, as well as be a season long problem in row rice. In these cases, I would recommend a fall application of Command®.
As always contact your county agent for more information. More information can also be found in fact sheets from the University of Arkansas Division of Agriculture including FSA 2149, 2171, 2191, and in the MP44 at www.uada.edu. ∆
DR. BOB SCOTT: University of Arkansas