Spring 1997 Permit Herbicide Trial on Direct Seeded Honeydew melons

James Peterson Cooperating with Texas Agricultural Extension Service, Experiment Station & U.S.D.A. including: L. Brandenberger, R. Wiedenfeld, J. Smart & E. Perez

Introduction:

One of the most serious constraints on melon production in South Texas is the competition that these crops face from different weed species. As melon growers have adopted new technology including drip irrigation and plastic mulch, competition from several weed species has decreased, but pressure from both yellow and purple nutsedge (Cyperus esculentus & C. rotundus) has continued to be a threat to production. Both of these weed species are a serious problem in vegetable crops that utilize plastic mulch culture because of their ability to puncture and grow through the mulch and the lack of control measures for them. Nutsedge will often over-grow melon production fields, competing with the crop for light, nutrients and water while at the same time greatly increasing production and harvest costs.

Objective:

Study objectives included determining the efficacy of Permit (halosulfuron-methyl) for the control of purple nutsedge (Cyperus rotundus) and determining any phytotoxic effects that the material may have on direct seeded honeydew melons.

Methods and Materials:

A herbicide study on direct seeded honeydew melons was conducted on a Rio Grande silt loam soil at Starrco Farm located in Starr County, Texas in the spring of 1997. Free standing plant beds utilized drip irrigation and black plastic mulch that was re-used from a watermelon crop grown the previous season (fall 1996). The field was treated with two applications of Roundup herbicide prior to planting for the control of nutsedge and other weeds, one in early January and one in early February. Honeydew melons were established in single rows with twelve inch in-row spacing on top of planting beds spaced on 80 inch centers and were direct seeded on February 15, 1997 to the cultivar Honey Brew. Drip irrigation was used for both seed germination and supplemental watering. Crop cultural practices were similar to those carried out on the adjacent commercial field.

Four treatments were included in the study (Table 1): 1) Permit at 0.75 ounces per acre rate applied one time; 2) Permit at 0.75 ounces per acre rate as two applications 21 days apart for a total rate of 1.5 ounces per acre; 3) Permit at 1.5 ounces per acre rate applied once and a non-treated check. Herbicide treatments were applied postemergent to the crop and weeds as a broadcast spray over the top of the plant beds with a four nozzle boom sprayer at an overall rate of 27 gallons of spray material per acre. Herbicide treatments 1, 2 and 3 were applied on March 20, 1997 and treatment 2 was reapplied the second time on April 10, 1997. The predominant weed species in the replicated trial was purple nutsedge. Four observational plots were established on the same dates using the same treatments as in the replicated study, but in an area where the predominant weed species was yellow nutsedge.

The replicated trial was arranged in a randomized block design with four replications and plots 25 feet long by 6.7 feet wide. All data were analyzed using Analysis of Variance and Duncan's multiple range test with P=0.05.

Phytotoxicity and efficacy were recorded on March 26, April 3, 10, 17 and May 6, 1997. Phytotoxicity was recorded as the percent damage to the crop compared to the untreated check. Efficacy was recorded as the percent of control to the existing weed population compared to the untreated check. Harvest data was recorded on May 16, 22, 27, 31 and included yield of marketable fruit and culls.

Results:

Significant differences were exhibited for efficacy on each day that data were recorded (Table 2). Efficacy ranged from 0% control for the non treated check to 97% for the treatment which utilized two applications at the 0.75 ounces per acre rate. Control of purple nutsedge developed gradually during the 45 day period following applications. On March 26, herbicide treatments ranged from 5.0 to 5.8% compared to 0% control recorded by the untreated check. Control of purple nutsedge increased each week and by May 6 varied from a low of 0% control for the non treated check to between 95 to 97% control for the herbicide treatments.

Phytotoxicity varied significantly for each of the five days that data was recorded and ranged from 0% damage on the untreated check up to 10% damage for the 0.75 ounce per acre rate (Table 2). Damage to honeydew vines was manifested as mottling to the leaf tissue and some stunting of the vines. The highest phytotoxicity ratings were recorded on March 26, six days after the initial Permit application. Over time, the recorded percent damage diminished to zero for all treatments except the treatment which received a second application of permit.

No significant differences were recorded between treatments for overall yield. Yields were somewhat lower for Permit treatments compared to the check during the first two harvests on May 16 and 22, 1997 (Table 4). Yields on May 27 and 31, 1997 were somewhat higher for Permit treatments. Total yield for all harvest dates combined was highest for treatments with one application of Permit on March 20, 1997, these had yields between 1611 and 1793 total boxes per acre. The treatment which included two applications of Permit had the lowest total yield.

Conclusions:

All application rates of Permit used in both the replicated and the observational plots resulted in a high percentage of control for nutsedge. In the replicated study, between 95 to 97 % control of purple nutsedge was attained with the use of Permit. In the observational plots, between 75 to 80 % control of yellow nutsedge was attained with the use of Permit (Table 3). Control of nutsedge was not immediate, but developed steadily over the six week period that data was recorded. This increased weed control over an extended period indicates the continued effectiveness and time delay for control to occur. Although chlorosis of the weeds occurred within a few days, death of the growing point and complete death of the weeds took up to four weeks to be completed. Phytotoxicity manifested itself as leaf mottling and some stunting and may have contributed to the lack of significant differences in overall yield between the untreated check and the herbicide treatments. Generally, yields were increased somewhat for those treatments that utilized Permit for control of nutsedge, but yields for the treatment which used two separate Permit applications were lower than those for the untreated check. Control of nutsedge may not only impact the crop this season, but could ultimately reduce weed control costs for future crops once nutsedge has been greatly reduced or eliminated.

The results of this study indicate that Permit postemergent herbicide has potential for control of nutsedge in cucurbit crops, specifically honeydew melons, but results from this study are only preliminary. Further study is needed to fully determine Permit's effect upon melon production and to provide data that may support labeling of this product for use in Texas Melon production.

Acknowledgments:

We would like to acknowledge the assistance given to us for the completion of this study by Mr. James Peterson. We also acknowledge the assistance given by Mr. Edelmiro Perez, Mr. Chewy Gonzalez, Mr. Carlos Rodriguez, Mr. Juan Bernal, and Mr. Venancio Gonzalez in the completion of this work.

The information given herein is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by Texas A&M or U.S.D.A. is implied.

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