Weed Control Efficacy and Crop Damage by. Carfentrazone-ethyl (Aim ) Herbicide on Sweet Corn

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1 Weed Control Efficacy and Crop Damage by Carfentrazone-ethyl (Aim ) Herbicide on Sweet Corn Jim E. Wyatt, Patricia Brawley, Robert M. Hayes and Craig H. Canaday Interpretative Summary Carfentrazone-ethyl caused an initial necrotic spotting on sweet corn leaves but had no effect on plant height or dry weight at 10 or 20 days after treatment. Redroot pigweed was suppressed but not controlled for the season. Entireleaf morningglory populations were insufficient for complete data collection but the herbicide showed promise in areas where plants were present. Annual grasses and yellow nutsedge were not controlled by carfentrazone-ethyl. Introduction Carfentrazone-ethyl is an herbicide approved for use on sweet corn. In past tests, it has been found to damage corn by causing necrotic spotting of leaves, breakage of the leaf midrib, and "buggy whipping" of leaves. This latter condition is thought to be due to application of the material when leaves are wet, resulting in concentration of the herbicide in the whorl. This test was conducted to study the effects of carfentrazoneethyl damage on sweet corn at four rates and at three stages of development and to determine the efficacy of the herbicide on weeds prevalent in the plots. Materials and Methods An experiment was conducted in 2002 at the West Tennessee Experiment Station, Jackson, to determine injury to sweet corn by application of carfentrazone-ethyl herbicide at different growth stages and to determine the effect of the herbicide on postemergence weed control sweet corn was planted April 16, Four-row plots were 20 ft long with rows spaced 2.5 ft apart and replicated four times; two center rows were used for data collection. Treatments were carfentrazone-ethyl at , , or lbs/a active with 0.25% X-77 spreader/sticker. Treatments were applied at 3-leaf, 5-leaf, or 7-leaf stages of sweet corn growth. Damage ratings on sweet corn were made at 3, 9, 17, 20, and 25 days after the 3-leaf stage treatment, 3, 11, 14 and 19 days after the 5-leaf stage treatment and 3 and 8 days after the 7-leaf stage treatment. Height of five randomly selected plants in each plot were measured from the soil surface to the apex of the smallest leaf at 10 and 20 days after each treatment. Five-plant samples were taken from each plot by cutting plants at the soil surface and oven drying to obtain estimates of dry weight at 10 and 20 days after each carfentrazone-ethyl treatment. Statistical analysis of plant height and dry weight data were conducted using relevant ANOVA procedures.

2 Results and Discussion No effect was seen in the growth and development of the corn after plants had recovered from the initial damage of the spray. No differences were found in plant height or dry weight between the control and the full rate of carfentrazone-ethyl (Table 1). Table I. Effects of carfentrazone-ethyl herbicide on sweet corn plant height and plant dry weight when applied at four rates and three stages of growth. rn stage at plication time Mean plant height (cm) 5-plant weight (g) 10 DAT z 20 DAT 10 DAT 20 DA eaf None eaf None eaf None

3 z Days after treatment Carfentrazone-ethyl caused considerable necrotic spotting on the leaves and some observed "buggy whipping" of the corn. Damage ratings for sweet corn were generally correlated with herbicide rates, particularly for the first 8 to 11 days after treatment (Table 2.) Damage was also progressively less as plants were more developed, with less damage on the 5- and 7-leaf treatments than on the 3-leaf treatment. By 17 to 25 days after treatment, corn appeared to have mostly recovered from the damage. Carfentrazone-ethyl had no effect on annual grasses or yellow nutsedge (Cyperus esculentus L.) and damage to these weeds was not rated. It did, however, cause considerable damage to redroot pigweed (Table 3). Damage was more severe on weeds with 2-4 true leaves and ratings were generally correlated with the rate of herbicide applied. Although many pigweed plants had symptoms of damage at 19 to 25 days after treatment, most were only suppressed and recovered sufficiently to cause major problems in the plantings in the latter part of the growing season. Table 2. Crop injury ratings for corn treated with carfentrazone-ethyl herbicide at 3-, 5-, and 7-leaf stages of growth. Corn stage at application time Crop injury rating z, days after treatment 3 days 9 days 17 days 20 days 3-leaf None 0 y days 11 days 14 days 19 days

4 5-leaf None days 8 days 7-leaf None z 0=no injury; 100=100% injury y Mean of four reps Entireleaf morningglory populations were not sufficient to obtain definitive control data for carfentrazone-ethyl (Table 4). Many plots did not have any plants. Where plants were present, the damage appeared to be sustained over a relatively long period and actually increased over time rather than decreasing as it had done on redroot pigweed. The herbicide needs to be evaluated in an area where entireleaf morningglory populations are high enough to get data from each plot over a period of time. Table 3. Injury ratings on redroot pigweed (Amaranthus retroflexus L.) treated with carfentrazone-ethyl herbicide at 3 corn growth stages. Corn stage at application time AMARE injury rating z, days after treatment 9 days 17 days 20 days 25 da 3-leaf None 0 y 0 0 0

5 days 11 days 14 days 19 days 5-leaf None days 8 days 7-leaf None z 0=no injury; 100=100% injury y Mean of four reps Table 4. Injury ratings on entireleaf morningglory (Ipomoea hederacea (L.) Jacq.) treated with carfentrazone-ethyl herbicide at 3 corn growth stages. Corn stage at application time IPOGH injury rating z, days after treatment 9 days 17 days 20 days

6 3-leaf None - x 0 y days 11 days 14 days 5-leaf None days 7-leaf None z 0=no injury; 100=100% injury y Mean of four reps x This weed species not present in these plots Copyright 1999 by The University of Tennessee. All rights reserved. This research represents one season's data and does not constitute recommendations. After sufficient data is collected over the appropriate number of seasons, final recommendations will be made through research and extension publications.