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.
It’s October already and soon crews will be thinning and weeding vegetable crops in the Yuma area. Automated machines for performing these tasks are commercially available and being used more and more. Due to significant research and development efforts being made in this area, the technology used for these machines is advancing rapidly. In the next series of articles, I will be discussing the developments made over the summer by automated machine manufactures and what growers in the Yuma area can expect for the upcoming season.
The first technology I’d like to discuss is the autonomous weeding robot “Dino” manufactured by Naïo Technologies (Fig. 1). Briefly, the robot is an 84” wide, self-piloted, mobile power unit equipped with camera guided cultivating tools.
Last season, Naïo demoed the robot for growers in the Yuma area. It was the first year the French based company had operations in the U.S. One goal of the demonstrations was to evaluate the machine in U.S. conditions and get feedback from growers about how the machine might best fit Arizona production systems. The company learned that Arizona vegetable production is very intense and fast paced. Machine productivity and durability were important issues for viability and domestic acceptance.
The company took heed of these observations. Over the summer, the battery that powers the fully electric robot was upgraded to provide 10 hours of operation before needing to be recharged. This improved work capacity from 8 acres/day to about 10 acres/day (work rate = ~ 1 acre/hour). To further address the capacity issue, the company imported three additional machines so that multiple machines could be operated simultaneously in the same field. The new machines are more robust, being equipped with higher torque drive wheel motors and a sturdier frame. The company is also in the process of switching to an improved camera guidance system that should enhance crop tracking ability and close cultivation performance. Some may be aware that the company has developed an award winning active in-row weeding tool that cycles cultivating blades in and out of the crop row (Link). The device is undergoing further testing and is planned for commercial release in mid-2021.
Machines will be available this fall in the Yuma area for demos or for hire as a weeding service. It will be interesting to see how these advanced robots perform and benefit weed management. If you would like assistance evaluating these machines or conducting performance trials, please feel free to contact me.
 Reference to a product or company is for specific information only and does not endorse or recommend that product or company to the exclusion of others that may be suitable.
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.
Results of pheromone and sticky trap catches can be viewed here.
We have started our Areawide Insect and DBM Trapping Network for the 2019-20 season.
We have added another trapping location in Bard, CA.
Area wide Insect Trapping Network VegIPM Update, Vol. 11, No. 20, Sep 30, 2020
Results of pheromone and sticky trap catches can be viewed here.
Corn earworm: Moth activity about normal for September but beginning to increase, particularly in Dome Valley and south Yuma Valley.
Beet armyworm: Moths remain active throughout the desert, especially in Texas Hill and Tacna growing areas- Staring to pick up in the south Yuma Valley.
Cabbage looper: Cabbage looper activity unusually low for mid-late September. Larvae just starting to show up in some fields.
Whitefly: Adult movement has been relatively light and about average for this time of year. Activity highest in Dome Valley.
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: No aphids have been caught on traps thus far. Normal for this time of year. Still early, anticipate they will begin to show up in 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.