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Harvest Weed Seed Control Promising for Italian Ryegrass

Italian ryegrass [IRG] is a problem winter annual weed in Midsouth wheat and a following soybean crop. The weed emerges in the fall and grows quickly and rapidly in winter and early spring. If not controlled, it will compete with a fall-planted wheat crop through harvest. It will then likely be an uncontrollable weed when soybean is planted following wheat harvest, and will significantly reduce soybean yield.

IRG has developed resistance to multiple herbicide sites-of-action, thus making it very difficult to manage when it is not controlled in the fall with tillage [where allowed] or effective herbicides. In fact, it is recognized as one of the most successful weed species at developing resistance to herbicides. Neither tillage nor herbicides will effectively control this weed if it becomes large as a result of no control measure(s) being applied before or soon after its emergence in the fall.

In the Midsouth, wheat and soybean are often doublecropped [Click here to access a doublecropping White Paper on this website]. Thus, IRG will need to be controlled at wheat planting to prevent it from becoming problematic in both the fall-planted wheat crop and a following soybean crop.

In a Feb. 28 advertorial [sponsored by FMC Corporation] titled “Boost Weed Control and Increase Wheat Yields–Get Ahead of Italian Ryegrass“ that appears in Progressive Farmer magazine, the issue of controlling this weed in a wheat crop is explored. The FMC herbicide Anthem Flex [carfentrazone-ethyl (Group 14) plus pyroxasulfone (Group 15)] is highlighted in the article as a residual herbicide for control of IRG. The article also provides guidance on the application timing of this PRE herbicide to wheat to control IRG since it is critical in relation to wheat seed germination.

In an article titled “Evaluation of Italian ryegrass seed dispersal prior to and at wheat harvest in Kentucky“ by Herman and Legleiter [Crop, Forage, and Turfgrass Mgmt., 2023;9:e20200,], results from a study that was conducted to evaluate the harvest weed seed control [HWSC] option as a control measure for IRG in a wheat crop are presented. The goal of HWSC research with any weed species is to reduce the soil weed seedbank, and the research reported in this article is exploring HWSC to do just that with IRG. Details of the research and its results follow.

•    The development of herbicide resistance in problem weed populations is increasing, and this is causing crop producers to look for alternative weed control methods. This is especially so for IRG.

•    HWSC is a nonchemical alternative method for weed control that is based on destruction of weed seed that are harvested with the crop and that pass through the combine. The objective of HWSC is to prevent harvested weed seeds from entering the soil weed seedbank.

•    In the study linked above, wheat fields with heavy infestations of IRG were selected. Overall, eight locations [3 producer fields and 1 experiment station field x 2 years–2020 and 2021] were used in the study.

•    Wheat was harvested on 26 and 25 June in 2020 and 2021, respectively.

•    At time of wheat harvest, more seeds of IRG were retained on the seed head [89%] than was found on the soil surface [11%]. The authors state that this retention rate is likely based on the location and its environment. Also, it is likely dependent on the time of wheat harvest in relation to IRG maturity.

•    The amount of IRG seeds that shattered at the combine header was significantly below that entering the combine. Unfortunately, this study’s findings were that less than 50% of the IRG seeds that entered the combine with the wheat were in the chaff portion. A significant percentage of IRG seeds made their way to the grain tank in both years. While this would have resulted in less IRG seed deposition to the soil, it likely would result in significant dockage for foreign matter in the harvested wheat seed that was delivered to the elevator for sale.

•    The finding that most of the IRG seed were retained in the seedhead at time of wheat harvest is significant, and certainly implies that those seed that entered the combine would not have been deposited on the soil to replenish the soil weed seedbank. However, a relatively smaller portion of the IRG seed entering the combine ended up in the chaff portion that would be available for destruction by an HWSC method. This means that the large amount of IRG seed in the grain tank would have resulted in significant foreign matter dockage at the elevator.

•    It is difficult for a combine to separate ryegrass seed from wheat seed during the threshing process. Thus, there needs to be work done to determine how to have most if not all of the IRG seed in the chaff portion so that all or most of the IRG seed entering the combine will be available for destruction by an HWSC method.

•    And finally, an effective strategy to control IRG early should be adopted so that IRG infestations at the time of wheat harvest and subsequent soybean planting are acceptably low. This will reduce the pressure on having to use HWSC methods to help manage IRG.

Click here for an article in Delta FarmPress [Jan. 4, 2021] titled “Managing Italian Ryegrass in Mississippi Soybeans” that provides various control options for IRG, and here for an article [Sep. 2022] titled “Investigating Italian Ryegrass Management Options” from the Soybean Research and Information Network [funded by the soybean checkoff].

Composed by Larry G. Heatherly, Mar. 2023,