May 5, 2021Summer Sanitation Is Important as Ever
To contact John Palumbo go to: jpalumbo@ag.Arizona.edu
Last year we had a lot of watermelon fields infected with Fusarium from Winterhaven to Yuma, Wellton, and Mohawk Valley. Rain, and overwatering of fields when plants set fruits might have contributed to the disease development.
Fusarium wilt of watermelon, caused by Fusarium oxysporum f. sp. niveum, is one of the oldest described Fusarium wilt diseases and the most economically important disease of watermelon worldwide. It occurs on every continent except Antarctica and new races of the pathogen continue to impact production in many areas around the world. Long-term survival of the pathogen in the soil and the evolution of new races make management of Fusarium wilt difficult.
Symptoms of Fusarium can sometimes be confused with water deficiency, even though there is plenty of water in the field. In Yuma valley we have seen fusarium problem in some overwatered fields.
Initial symptoms often include a dull, gray green appearance of leaves that precedes a loss of turgor pressure and wilting. Wilting is followed by a yellowing of the leaves and finally necrosis. The wilting generally starts with the older leaves and progresses to the younger foliage. Under conditions of high inoculum density or a very susceptible host, the entire plant may wilt and die within a short time. Affected plants that do not die are often stunted and have considerably reduced yields. Under high inoculum pressure, seedlings may damp off as they emerge from the soil.
Initial infection of seedlings usually occurs from chlamydospores (resting structure) that have overwintered in the soil. Chlamydospores germinate and produce infection hyphae that penetrate the root cortex, often where the lateral roots emerge. Infection may be enhanced by wounds or damage to the roots. The fungus colonizes the root cortex and soon invades the xylem tissue, where it produces more mycelia and microconidia. Consequently, the fungus becomes systemic and often can be isolated from tissue well away from the roots. The vascular damage we see in the roots is the defense mechanism of the plant to impede the movement of pathogen.
Disease management include planting clean seeds/transplants, use of resistant cultivars, crop rotation, soil fumigation, soil solarization, grafting, biological control. An integrated approach utilizing two or more methods is required for successful disease management.
Due to a lack of effective selective, post-emergence herbicides, most vegetable crops are hand weeded following cultivation to remove in-row weeds. This operation is costly and finding labor to perform the task has become increasingly difficult. An alternative is to use automated/robotic machines for in-row weeding. These machines have been around for quite some time; the first “modern” units were commercialized in 2008. Since then, at least six companies have introduced machines and offer units for sale and/or automated weeding as a service in Yuma, AZ.
Despite these innovations and efforts, adoption of automated weeding machines has been limited. One reason for this is that weed control is only partial, and follow up hand weeding is often necessary. All commercialized automated weeders utilize metal blades that move in and out of the crop row to cultivate weeds between individual crop plants as the machine moves through the field. As such, soil disturbance is high and weeds close to crop plants cannot be effectively removed without injuring crop plants. In a two-year study (Lati et al., 2016), we found that mechanical automated weeders removed about 2/3rds of in-row weeds. The majority of uncontrolled weeds (~ 1/3rd) were observed to be within about 1” of the crop plant.
To address the lack of precision of current automated weeding machines, we developed two high speed, centimeter scale resolution sprayers to spot apply herbicides to weeds with minimal off-target spray while traveling speeds that are viable for commercial farming operations (2 mph). The first is a high precision (sub-centimeter scale resolution) sprayer designed for spot spraying cotyledon stage weeds in leaf lettuce crops. The second is a spray assembly designed for controlling in-row weeds in vegetable crops that are close to crop plants (1-cm scale resolution). We tested the device in 2019 in the laboratory and found that weed control efficacy was greater than 95% (3 species), percentage of off-target spray was less than 3% and no crop injury was observed. A link to action videos of the device in action is provided at the link below. Future work includes seeking funding, and industry partners for integrating the devices with imaging systems to develop a high precision, automated/robotic weeding machine for vegetable crops.
Lati, R.N, Siemens, M.C., Rachuy, J.S. & Fennimore, S.A. (2016). Intrarow Weed Removal in Broccoli and Transplanted Lettuce with an Intelligent Cultivator. Weed Technology, 30(3), 655-663.
High Speed Centimeter Scale Resolution Sprayers for Precision Weed Control – Video Link: https://www.youtube.com/watch?v=TFja9FmVjJI
To contact Mark Siemens go to: email@example.com
The Yuma County Leaf Wetness Network remains in place for the 2018/19 vegetable season. Growers and PCAs may access information generated by the network by entering the following internet address: http://188.8.131.52:460
Upon entering the address above, you will be transferred to internet page that provides a series of tabs at the top of the page. Simply click on the tabs to access the information of interest.
Area wide Insect Trapping Network VegIPM Update, Vol. 11, No. 21, October 14, 2020
Results of pheromone and sticky trap catches can be viewed here.
Corn earworm: Moth activity is above normal for early October ad has been steadily increasing since mid-September, particularly in Dome Valley and south Yuma Valley.
Beet armyworm: Moths remain active throughout the desert, especially in Texas Hill and Dome Valley growing areas.
Cabbage looper: Cabbage looper activity remains unusually low for early October, likely a result of unusually hot weather. Larvae just starting to show up in some fields.
Whitefly: Adult movement has been about average for this time of year. Activity highest in Wellton and Roll near fall melons.
Thrips: To date, thrips activity has been seasonably low at all trap locations; most activity found in Bard. Numbers beginning to slowly trend upward
Aphids: Aphids have been caught in only one trap thus far (Bard). Normal for this time of year. Still early, anticipate they will begin to show up in heavier numbers in mid-late October.
Leafminers: Adult activity below normal for September, but moderate numbers caught in Wellton and south Gila Valley in areas where cotton was recently harvested and disked under.