May 5, 2021Summer Sanitation Is Important as Ever
To contact John Palumbo go to: jpalumbo@ag.Arizona.edu
Although it is not vigorous or vegetative, Shepardspurse is one of the most widespread and difficult to control broadleaf weeds worldwide. I used to think that it spread when there was more alfalfa here and because it is not controlled with 2,4-DB (Butyrate & Butoxone) but it has continued to spread in vegetable crops. It likely has become worse each year because of its growth habits more than its tolerance to herbicides. It germinates from on or just below the soil surface. Herbicides that move or are placed below the surface often miss it. It is difficult to control with Kerb, for instance, because it leaches easily with overhead sprinklers. The seed is less than 0.1 inch in diameter and moves easily in wind and water. It is very small, and the cotyledon leaves are hardly ever seen. By the time you see it, it is at the 3 or 4 leaf stage. It grows rapidly in a rosette that is low to the ground and often covered by the crop. Herbicide coverage is difficult. It soon puts up a thin seed stalk and several seed pods (“purses”). Unlike many annual broadleaf weeds, it can produce several generations in one season. It can grow year round in many regions but has a difficult time surviving the summers in the low desert.
Damping off is a common problem in spinach. This season we have observed the occurrence of the disease from Imperial valley, to Yuma and all the way to Wellton.
Symptoms of damping‑off and root rot consist of poor seed germination, preemergence death of seedlings, postemergence death of newly emerged seedlings, stunted plants, yellowed lower leaves, general poor growth, wilting, and eventual collapse and death of older plants. The upper taproot may be girdled by a necrotic lesion, or the tip of the taproot may be necrotic. In severe cases, nearly all roots may be girdled or rotted off. Damping-off is problematic in spinach production areas throughout the world. Severity is influenced by cultivar, soil texture, irrigation, and pathogen populations. Severe damping-off is associated with clay or poorly draining soils with a history of frequent spinach production. While all stages of spinach can be infected by root rot organisms, newly emerging plants and young seedlings are very susceptible.
Symptoms are more prominent in areas with poor drainage. These spinach problems are caused by a complex of pathogenic soil fungi that include one or more of the following: Fusarium oxysporum, Pythium (several species), and Rhizoctonia solani. These fungi are present in most soils and can get aggressive and cause loss when the environment is favorable. However, aboveground symptoms of plants that are overwatered are similar to symptoms of root rot. Excess water can damage roots, causing tan to brown, water‑soaked symptoms on roots even if no pathogen is present.
Plant spinach in well draining soils. Prepare seed beds so that even, rapid germination is enhanced. Carefully manage the irrigation schedule to prevent flooding and saturated soil conditions. Plant seed that is treated with fungicides and fumigate the beds. Preplant application of mefenoxam will only control damping-off caused by Pythium. Avoid planting consecutive spinach crops and practice good crop rotation.
Always remember the disease triangle, the necessity of a susceptible host, the favorable environment, and virulent pathogen. To create unfavorable environment avoid overwatering, do light but frequent irrigation to avoid standing water in the field, schedule watering in the morning or earlier part of the day. Addition of soil amendments to increase microbial activity can be helpful.
Mark C. Siemens
Vol. 12, Issue 9, Published 5/5/2021
Area wide Insect Trapping Network VegIPM Update, Vol. 11, No. 22, October 28, 2020
Results of pheromone and sticky trap catches can be viewed here.
Corn earworm: Moth activity is about average for mid-October, particularly in Dome Valley and south Yuma Valley.
Beet armyworm: Moths remain active throughout the desert, especially active in Tacna and Dome Valley.
Cabbage looper: Cabbage looper activity remains unusually low for early October, likely a result of unusually hot weather. Larvae are yet to show up in many fields.
Whitefly: Adult movement has been about average for this time of year. Activity highest in Tacna near fall melons.
Thrips: To date, thrips activity has been seasonably low at all trap locations; activity increased significantly in Roll.
Aphids: Aphids beginning to show in most traps along the Colorado River (Bard, Gila, Yuma) which is normal for this time of year. Recent high winds may begin to disperse them throughout the area.
Leafminers: Adult activity below normal for September, but high numbers caught in Wellton in areas where melon harvest has commenced.