eed control is an important aspect of commercial watermelon production. In the past, producers have struggled with this aspect of crop culture, and have had few new technologies available for use on this important crop in recent years. Control of both yellow and purple nutsedge has particularly been a problem when producers have adopted the use of drip irrigation and black plastic mulch to increase yields and the quality of the crop.
Nutsedge is a serious problem species because it has the capability to puncture and grow through black plastic mulch. This greatly adds to the cost of producing a crop, due to the added cost for weeding, harvest, and the associated loss of yield.
Halosulfuron-methyl “Sandea” is a new herbicide that can control both species of nutsedge and several other weeds. It is a “reduced risk” material that, when utilized at low rates, can control these serious weed competitors with less environmental impact than many currently labeled compounds.
Study objectives included evaluation of Sandea, applied in combination with other materials at four different rates, to determine effectiveness for weed control and its potential for damage to crops following its use.
A watermelon herbicide study was completed at the Bixby, Oklahoma Vegetable Station during the summer of 2001. The study included a non-treated check, a weeded check, and 18 weed-control treatments utilizing Sandea (Halosulfuron-methyl), Curbit (Ethalfluralin), Alanap (Naptalam), Prefar (Bensulide), and Command (Clomazone).
Treatments were replicated four times in a randomized block design in plots 33 feet long by 10 feet wide. Plots were planted on May 17, 2001 to the watermelon cultivar ‘Jubilee’.
Phytotoxicity and efficacy ratings were taken on five different dates, beginning on June 7th and ending on July 17, 2001. Plots were harvested on August 6, 2001.
Following completion of the spring study, a carry-over study was conducted to determine the potential damage to subsequent crops. Plots were planted on September 11, 2001 to four different crop species: spinach, broccoli, wheat, and cabbage. Crop emergence and stunting were recorded on October 1 and 24, 2001.
Phytotoxicity varied significantly between treatments on all days except for July 17th. The second rating on June 12, 2001 recorded the highest levels of crop damage of the ratings that were made. Phytotoxicity on June 12 was 0, 0, 62.5, 48.8, and 66.3 percent damage, respectively, for the untreated check, weeded check, Sandea pre @ 0.048, Sandea 0.024 + Curbit 1.5, and Command 0.15, + Curbit 0.56 + Sandea 0.032 pre. Generally, ratings were highest early in the season, and decreased as time passed, to less than 10 percent damage for all treatments on the last date that ratings were recorded.
Efficacy ratings for control of pigweed varied significantly for each of the five ratings. All herbicide treatments provided higher levels of pigweed control when compared to the untreated check. In addition, all herbicide treatments provided significantly higher levels of carpetweed control, as compared to the untreated check, (see Table below).
Overall yield did not vary significantly among herbicide treatments. However, all herbicide treatments nearly doubled the yield produced by the untreated check, and equaled that from the hand-weeded plots.
In the carry-over phase of the study, percent emergence did not vary significantly for spinach and wheat. However, pre-emergence applications of Sandea did cause emergence reductions for broccoli and cabbage in the range of 20 to 20 percent.
Stunting was observed to vary significantly for broccoli, cabbage, and spinach.
Based upon the results of the study, it appears that Sandea, as a pre- or post-emergence treatment, by itself and in combination with other materials, does have good potential for controlling pigweed and carpetweed in commercial watermelon crops.
Previous work in South Texas by Dr. Brandenberger showed Sandea to provide excellent control of both yellow and purple nutsedge. Although it works well in watermelon, following Sandea with broccoli, cabbage, or spinach did result in some reduction in stand and serious stunting of these crops from carry-over.
Sandea had little effect upon the wheat that was planted following the spring study.
The authors feel that further study of Sandea, particularly regarding carry-over effects upon crops that follow its use, is warranted.
