C.O.R.N. Newsletter: 2025-28

Fall is an important time of year for managing perennial weeds in forage crops, especially pastures. Some weed issues were exacerbated in 2025 due to last year’s drought, and we’ve seen many pastures and hayfields with high levels of hemp dogbane, milkweed, Canada thistle, and others. Perennial species can be particularly hard to control since their root systems and other underground structures allow them to regrow quickly after their above ground structures are killed. Fall is an important window for perennial species control, since actions taken now can reduce the amount of energy they store underground for next year.

Frequent mowing is a type of mechanical weed control that helps deplete the amount of carbohydrates that plants have stored in their root systems. Over time, plants that are mowed frequently will be less able to grow back quickly. Using a systemic herbicide in conjunction with mechanical weed control can further reduce a perennial weed’s ability to bounce back in spring. Systemic herbicides are able to move from where they are sprayed on the plant surface to the underground portion of plants. Fall is one of the most effective times of year for systemic herbicide use on perennial plants as the plants will actively move the herbicide throughout the root system as they fill their carbohydrate storages, but they must be used when plants are still actively growing. Optimal timing will be a few weeks after the last cutting, but before hard frosts begin—in most years, that’s sometime in September for Ohio. Control is more effective if perennial weeds are allowed to regrow to around 6-12 inches tall before applying herbicides.

Some weeds that were of particular concern in 2025 were hemp dogbane, common milkweed, Canada thistle, pokeweed, and horsenettle. Most of these weeds are more responsive to herbicides early in the season, before they reach 8 inches in height. But, another opportunity for control is in fall. Systemic herbicides with good control on hemp dogbane and Canada thistle include dicamba (Clarity, others) and triclopyr (Remedy Ultra). Glyphosate is the best option for milkweed, although it will also have partial control with Remedy Ultra. Canada thistle, another aggressive perennial, responds best to fall applications of glyphosate, clopyralid (Stinger), or 2,4-D + dicamba, especially after light frosts when the plant is still translocating nutrients to its roots. Cultural practices like maintaining competitive forage stands can also suppress thistle growth, and dense forages can also reduce nightshade emergence. Pokeweed control requires removal of the entire taproot for mechanical success, though herbicides like glyphosate and dicamba are effective when applied during flowering. Spot treatments or cut-stump applications are advised near desirable vegetation.

Other troublesome weeds include cocklebur, which can be suppressed with early mowing and pre-emergent herbicides; horsenettle, which responds to Crossbow (2,4-D plus triclopyr) or triclopyr during bud to bloom stages; quackgrass, which is best treated with glyphosate in late fall; and multiflora rose, which can be managed with metsulfuron (Escort) or Crossbow during fall or bloom periods. Each of these species requires a tailored approach, but fall remains one of the most effective seasons for long-term perennial weed control in forage systems.

Herbicide options will vary based on the species you are trying to preserve in your pasture, the types of weeds you have, and your application method options. In grass pastures that lost their clover stands in last year’s drought, or elsewhere you plan to frost-seed clovers this winter, you have the option of using herbicides that are grass-safe but not legume-safe, including dicamba, clopyralid, aminopyralid (Milestone), picloram (Tordon, ingredient in Surmount), and 2,4-D. As always, pay close attention to herbicide labels to avoid as much as possible any use restrictions on treated hay and to prevent unintended damage to desired vegetation.

Farmers may be interested in winter rye for grain to meet local demands and niche markets. Over the past five years, we have conducted several experiments on hybrid rye, including variety selection, planting date, seeding rate, and spring nitrogen application rate. Available resources include:

1. Hybrid Rye Grain Yield Compared to Other Small Grains. In Ohio, soft red winter wheat is the predominantly produced small grain, with around 500,000 acres planted each fall. Over a three-year period, we compared soft red winter wheat grain yield to other small grains, including hybrid rye. Across the three years, soft red winter wheat yielded the greatest, averaging approximately 90 bu/acre while hybrid rye yielded nearly 80 bu/acre and open-pollinated rye yielded an average of 70 bu/acre. For the full set of results, see this FactSheet: https://ohioline.osu.edu/factsheet/anr-0154
2. Planting Date and Seeding Rate. During the 2021-2022 and 2022-2023 growing seasons, we evaluated hybrid rye planting date and seeding rates in four states (Kentucky, Ohio, Wisconsin, and Minnesota). In Ohio, across planting dates and seeding rates, grain yield was generally high, averaging approximately 90 bu/acre. Maximum grain yield occurred when rye was planted within the two-week period following the county Hessian fly-safe date and at a seeding rate of at least 800,000 seeds/acre. For a full description of this experiment, please see this publication in Crop, Forage & Turfgrass Management: https://acsess.onlinelibrary.wiley.com/doi/10.1002/cft70052
3. Hybrid Rye and Nitrogen Rate. During the 2024-2025 growing season, an experiment was conducted to identify the optimum spring nitrogen application rate for three rye hybrids. First year results indicated that approximately 80 lb N/acre optimized grain yield at the Western Agricultural Research Station in Clark County while 120 lb N/acre optimized grain yield at the Northwest Agricultural Research Station in Wood County. (However, the nitrogen rate that maximizes grain yield may not maximize profitability.) There was no hybrid by nitrogen rate interaction, which means nitrogen application rate did not need to be different for the three hybrids. Lodging was variable depending on location, with no lodging in Wood County and up to 70% of plants lodged in Clark County. Higher lodging was associated with higher nitrogen application rates. First-year results are preliminary, and the study will be repeated during the 2025-2026 growing season. Year 1 results can be found here: https://stepupsoy.osu.edu/sites/hcs-soy/files/Hybrid%20Rye%20Report%20Page%201_0.pdf

Recently, Curvularia leaf spot of corn was confirmed in research and demonstration plots in Central Iowa, the furthest north it has been observed so far. This foliar disease is caused by the fungus Curvularia lunata and was first reported in the U.S. in 2017 and since then has been confirmed in Missouri, Louisiana, Kentucky, and now Iowa. Its effect on corn yield in the Midwest is unknown, but it can cause significant losses in tropical areas. It has not been reported in Ohio yet, but it is important to keep an eye out for this emerging corn disease during your late-season scouting efforts.   

Especially in fields of continuous corn using conservation tillage practices, look for very small, round, tan lesions on leaves in the mid to upper canopy. Lesions have a white center with a water-soaked margin at first, then later develop an orange-brown margin surrounded by a yellow halo (Figure 1). Symptoms may be easily mistaken for other corn diseases such as eyespot or gray leaf spot. Eyespot is more commonly observed before pollination and under cool, wet conditions. Whereas the fungus causing Curvularia leaf spot requires warm, humid conditions. Early gray leaf spot symptoms may also look like Curvularia leaf spot, but gray leaf spot lesions will elongate as they develop, and Curvularia will stay round.

If you suspect Curvularia leaf spot, please submit a sample to the C. Wayne Ellett Plant and Pest Diagnostic Clinic (CWE-PPDC) located in Wooster, Ohio. See sample submission instructions on the CWE-PPDC website at https://ppdc.osu.edu/. You may also contact State Specialist Dr. Pierce Paul at paul.661@osu.edu (330-347-5878) or CWE-PPDC Director and diagnostician Dr. Francesca Rotondo at rotondon.11@osu.edu or ppdc@osu.edu (330-263-6721).