Introduction:
According to the most recent statistics, the United States (US) was the world's sixth largest producer of melons, with a significant proportion (>50%) of the country's production occurring in California. In 2011, 36,900 and 10,300 acres of cantaloupes and honeydews were harvested, respectively. Combined, the crops were valued at an estimated $227 million, which is an increase of 29% over 2010.
Weed control in melons is difficult due to the vining nature of the crop (which can prohibit mechanical cultivation) and the limited availability of safe and selective preemergence (PRE) and postemergence (POST) herbicides. Early-season weed control is crucial in order to prevent competitive interference between the crops and weeds, which can reduce crop yields; late-season weed management is also important as weeds can harbor pests and pathogens which can adversely affect fruit quality. Weeds can also reduce harvest efficiency, which can result in increased labor costs.
Previous Work at UCD:
Research scientists at the university of California, Davis, have focused on characterizing the crop injury and weed control potentials of various herbicides that are not currently labeled for use in cantaloupes and honeydews (either in California or in melons across the US) including: metolachlor, flumioxazin, sulfentrazone, pendimethalin, fomesafen, clomazone and linuron.
2010: In general, cantaloupe was tolerant of linuron and flumioxazin (up to a maximum of 8% injury) and moderately-injured by pendimethalin, metolachlor, sulfentrazone and fomesafen (up to a maximum of 38% injury). Sulfentrazone was the best product in terms of broadleaf weed management (99 to 100% control), with control lasting through harvest. Metolachlor and pendimethalin were the best materials for grass control (88 to 99% control). Cantaloupe and honeydew yields were highest using sulfentrazone, despite the early season injury, indicating that weed control was more important than melon tolerance in terms of yield.
2011: Cantaloupe exhibited a tolerance to flumioxazin, pendimethalin, sulfentrazone, metolachlor and fomesafen, but was seriously injured by linuron (100% crop loss); linuron was applied at double the rate employed in 2011. Linuron was the best in terms of broadleaf weed control (79 to 100% control), whereas clomazone (51 to 96% control) and pendimethalin (51 to 81% control) were the best materials against grasses. Cantaloupe and honeydew yields were highest in the sulfentrazone and metolachlor treatments (40 to 62 fruit per plot), despite their inconsistent control of broadleaf weed (15 to 98% control) and grass (18 to 65% control) weeds in 2011.
2012: In 2012, a combined treatment of metolachlor plus sulfentrazone was attempted, as each of these materials has been shown to be effective and moderately safe in previous years, in an attempt to maximize weed control. However, significant injury (40 to 70% phytotoxicity) was observed suggesting that the use rates of one or both of these materials may need to be reduced to improve crop safety.
2013 Objectives:
The objective of this current study was to evaluate the effects of pre-emergence (PRE) herbicides, along with a layby herbicide, on melon safety and season-long weed control.
Materials and Methods:
The 2013 research trial was seeded on 6 June at a research farm on the University of California–Davis campus. Soil at the site is a fine, silty loam (Yolo series). Both cantaloupe (‘Oro Rico' and ‘Yosemite') and honeydew (‘Saturno') melons were evaluated in the study. Each main plot consisted of three sets of two-row sub-plots (one set for each type of melon) that were 30 feet in length and were on a 60 inch spacing. Every other bed was planted, allowing for 120 inches between seed lines. Herbicides in the trial included: ethalfluralin (Curbit at 4 pt/A), clomazone (Command at 0.55 pt/A), ethalfluralin plus clomazone (Strategy at 4 pt/A), halosulfuron (Sandea at 0.75 oz/A), metolachlor (Dual Magnum at 1.33 pt/A), sulfentrazone (Zeus at 3.2 oz/A) and trifluralin (Treflan at 1.5 pt/A). Except for the Treflan, which was applied at layby, herbicide applications were made after planting (using a backpack sprayer calibrated to 20 GPA), but prior to crop emergence, and incorporated with sprinkler irrigation. Crop size and weed cover and density were evaluated weekly to bi-weekly for the first 6-8 weeks of the experiment. Fruit were harvested from each plot at maturity.
A Note About Herbicide Selection:
Ethalfluralin (Curbit) was selected for use in the study because it is the predominant PRE-applied herbicide in California melons. Although halosulfuron (Sandea) is an excellent product for the suppression of nutsedge in melons, rotation restrictions may limit its use in California. Growers report some delay in fruit set when using halosulfuron. Both served as performance standards in this trial.
Clomazone (Command) is labeled for use in melons in every state, except California. In general, clomazone has proven to be relatively safe on cantaloupe and honeydew melons, although early season injury may occur at higher rates (T. Lanini: Personal observation 2010, 2011). Additionally, clomazone can sometimes be effective at controlling small-seeded broadleaf weed species in California (T. Lanini: Personal observation 2010, 2011). It served as an industry (country-wide) standard in this trial.
Sulfentrazone (Zeus) is an"A"priority product being investigated for use in melons in the IR-4 program. It is not registered. In 2010 and 2011, sulfentrazone provided the best control of small-seeded broadleaf weed species in UC-Davis trials (T. Lanini: Personal observation 2010, 2011). Despite the occurrence of some early season crop injury, cantaloupe yields were greatest in the sulfentrazone plots in both 2010 and 2011 (T. Lanini: Personal observation 2010, 2011). FMC, the product manufacturer, has funded plant-back studies in preparation for sulfentrazone registration on crops in California.
S-metolachlor (Dual Magnum) has also been ranked as an"A"priority product for use in melons. It is not registered. It caused some temporary, early-season injury tomelons in 2010 trials conducted at UC-Davis, but appeared relatively safe in 2011 (T. Lanini: Personal observation 2010, 2011). S-metolachlorhas consistently provided good to excellent nutsedge control, and has proven to be an effective product for the management of annual grasses, pigweeds and lambsquarters (T. Lanini: Personal observation 2010, 2011). In both 2010 and 2011, melon yields from S-metolachlor treated plots were statistically similar to yields achieved in plots treated with sulfentrazone (T. Lanini: Personal observation 2010, 2011).
Results:
The lowest levels of weed control occurred in the Command plots and the untreated check (8-87% cover 3-6 weeks after crop emergence). All other herbicide programs provided good to excellent control of weeds (0-11% cover) for up to 6 weeks after crop emergence. The greatest amount of crop injury (plant sizes were sometimes reduced by >50%) was observed in the Zeus plots, which also provided the best weed control. Herbicide injury was still evident in the Zeus plots at 5 weeks after crop emergence. Control plots, at 5 weeks after emergence, showed reduced plant growth as the result of significant weed competition. Crop yields (total fruit numbers and weights per plot) were the lowest in the check and Command plots (Mean of both treatments across all three melons: 86 fruit/plot, 312 lbs/plot), where weed cover was the greatest. Despite significant early season injury, Zeus-treated plots (Mean across all three melons: 109 fruit/plot, 380 lbs/plot) yielded better than the control treatment and as well as the Curbit (Mean across all three melons: 101 fruit/plot, 370 lbs/plot) standard. Strategy, Sandea and Dual Magnum performed as well as the Curbit standard.
Conclusions and Future Research:
- The lowest levels of weed control, across all melons, occurred in the Command plots and the untreated check. All other herbicide programs provided good to excellent early-season weed control
- The greatest amount of crop injury was observed in the Zeus plots, which also provided the best weed control. Herbicide injury was still evident in the Zeus plots at 5 weeks after crop emergence. Control plots, at 5 weeks after emergence, showed reduced plant growth as the result of significant weed competition.
- Cantaloupes were more sensitive to herbicides than was honeydew.
- Crop yields (total fruit numbers and weights per plot) were lowest in the check and Command plots, where weed cover was the greatest.
- Despite significant early season injury, Zeus-treated plots yielded better than the control and as well as the Curbit standard.
- With respect to the combined effects of weed control, visible crop injury and yield, Strategy, Sandea and Dual Magnum performed as well as the Curbit standard.
- Future research will focus on: 1) the use of soil amendments in an attempt to prevent herbicide leaching into the seed zone (thereby reducing subsequent crop injury), 2) the use of Zeus at lower rates and in combination with other herbicides for weed control in melons, 3) evaluating the effects of soil type (sandy vs. loamy) and irrigation strategy (furrow vs. drip) on herbicide (particularly Dual Magnum) safety and performance, 4) comparing herbicide performance and safety in seeded and transplanted melons, 5) characterizing the effects of herbicide carryover and drift on melon injury and yield and 6) evaluating ‘non-melon' herbicides for crop safety.
Acknowledgement:
The Authors would like to thank The California Melon Board for Funding this project; Jim Jackson and farm support staff for their assistance with the establishment and maintenance of the trial; and Oscar Morales, Seth Watkins, Marcelo Moretti, Andrew Johnson, Rolando Mejorado and Matthew Linder for their help with this project.
The full report can be accessed below.
Attached Files: