Although the 2018 corn soybean harvest completion extended a few weeks longer than normal, mostly cover crops planted this fall have higher growth compared to last year. Among the mix of cover crops selected, cereal rye (Secale cereale) is likely the most common species grown in central Nebraska. This grain species is closely related to other cereal or small grain plants, and mature plant grain can be used to make rye breads.
Sometimes producers confuse ‘annual’ (Lolium multiflorum) also called ‘Italian’ rye grasss with ‘cereal’ rye; and Bruce Anderson, Nebraska Extension Forage Specialist, says that planting the wrong rye species can be an expensive mistake. Botanically, the annual rye grass and Italian rye grass plants are similar to cereal rye.
However, in the forage & cover crops context, these species are very different; and it is much more difficult to terminate the annual or Italian (forage-type) growth in the Spring compared to the cereal (grain-type) rye species. Even cereal rye producers may face challenges of growing the cover crops long enough for adequate growth without reducing yields regarding the subsequent spring planted cash row crops.
The term ‘annual’ & ‘Italian’ rye grass usually refers to cultivars used for turf and forage. These rye grasses are not true annuals; and during mild winters these plants can survive like a perennial. In Nebraska, spring plantings grow rapidly and can produce seed heads with each growth cycle. Growth rates slow during the heat of summer, and the plants usually die over winter. ‘Italian’ rye grass tends to grow like a biennial. They produce mostly high quality leaves while growing vigorously throughout summer and fall depending on moisture. They frequently survive mild winters and produce seed heads the following spring. These cultivars can be used to thicken winter-injured forage stands, as a perennial forages companion crop or as a temporary high quality forage.
Generally, cover crops are used in cropping systems for soil (root growth) enhancement and protection against wind & soil erosion without decreasing row crop yields. Thus, cover crop growth is likely terminated about two weeks ahead of row crop (corn & soybean) planting. Whereas, if the same plant species are planted as grazing forage, target cover crop termination dates are delayed with some row crop yield loss accepted as a trade-off for forage produced. Nebraska Extension research has revealed that cereal rye forage production can double when provided just 2-3 more weeks for spring growth.
According to the NRCS Environmental Quality Incentives Program (EQIP) rules, winter annual cover crops planted in western and central Nebraska should be terminated at least 15 days prior to planting a subsequent cash crop. These guidelines pertain to cover crops planted into non-irrigated fields to promote best management practices that minimize risk of yield loss due to lack of soil water.
Even if corn producers are not receiving EQIP financial incentives to adopt new conservation practices; early cereal rye termination (when the plant heights reach 6-8” or 10-14 days ahead of corn planting) is highly recommended. When spring rye development shifts from vegetative to reproduction growth (jointing stage), their carbon to nitrogen (C:N) ratios change to higher carbon and lower nitrogen content. Then, the declining mature plants do not have enough nitrogen to meet the nitrogen demands of soil microbes during the residue decomposition process. As a result, new seedling may have a short-term nitrogen deficiency combined with an allellopathic chemicals reaction delaying young corn plant development. Thus, cereal rye root systems, which absorb much of the freely available soil nitrogen, may have a positive suppression of weeds development; but negative short-term effects regarding new corn crop development.
For early cereal rye chemical applied termination, glyphosate herbicides are commonly used. Please note that while these products have worked well on cereal rye; they may need repeat applications to control annual or Italian rye grasses especially when Spring temperatures are less than 50°F. Further, repeated use of glyphosate could increase herbicide resistance with winter annual weeds. Therefore, alternative herbicides or tank-mixing glyphosate with other burndown products such as 2,4-D, dicamba, saflufenacil
(Sharpen®), paraquat (Gramozone®); and/or glufosinate (Liberty®) may help reduce weeds developing herbicide resistance; even though, herbicide input costs will increase.
More information regarding cover crops is available through the Nebraska Extension website: https://cropwatch.unl.edu or your local Extension office. Cover crops will also be a highlighted topic during 2019 Nebraska Extension WC Crop Production Clinics at
the following locations: Grand Island (Jan. 23); Holdrege (Jan. 25); and Kearney (Jan. 28– 29).