What is in this article?:
- Whitefly adults are now easier to find on spring melons - damage from feeding is a concern;
- Effectively managing powdery mildew with fungicides is best achieved by an initial application ideally before but not later than the first visible disease detection;
- Dodder is a difficult weed to control – 15 species are found in Arizona.
By Barry Tickes, UA Area Agriculture Agent
Dodder has been a difficult to control weed in the Yuma County area for a long time but it seems worse in recent years. It is listed as one of the 10 most problematic weeds in the U.S. by the Department of Agriculture.
There are more than 150 species of dodder. Fifteen of these are found in Arizona, three are common, and one field dodder, Cuscuta campestris, is a problem in the lower Colorado River region. It can be a problem on many crops grown during the summer months including melons, safflower, asparagus, sugar beets, beans, alfalfa, and others.
Dodder is an unusual weed. It is a parasitic annual with no leaves or roots after it is attached to a host. It obtains all of its energy from the attached plants. Dodder germinates near the soil surface and lives off food reserves in the seed. It must attach to a host within five to 10 days or it will die.
After it has found a suitable host, it produces adventitious roots called haustoria that grow into the vascular system of the host plant. After it is attached, the lower portion of the dodder seedling dies and all contact with the soil ends.
Dodder seed is small - about 1/16 inch in diameter - and germinates in the spring or summer once the soil temperature reaches about 60 degrees. Each plant can produce several thousand seeds.
The seed is hard and less than one-third can germinate the following season. The remainder can remain dormant but viable for 20 years or more. The seed is small and light enough to float in water and blow in the wind.
Most of the movement is probably from contaminated crops, seed, and equipment. Controlling this weed starts by reducing seed movement into an area. Most states and countries have laws that prohibit the import of dodder seed.
Only certified seed should be planted. A major cause for dodder spread in Arizona is non- certified alfalfa seed. Once dodder is in a field, annual crops that are poor hosts can reduce the spread of this weed. Poor host crops include grasses, grains, and other monocots. Other weeds can serve as hosts and should be eliminated.
Pre-emergent herbicides can be effective in keeping this weed from becoming established. Post-emergence herbicides should at least temporarily destroy the host.
Perennial crops including alfalfa can be temporarily burned to the ground with contact herbicides including Gramoxone, Chateau, or Scythe plus an adjuvant. Dodder can be selectively killed with glyphosate in Roundup Ready Alfalfa.
The most effective control is with pre-emergent herbicides. These include trifluralin, pendimethalin, benefin, Dacthal, and others.
When the herbicide levels have dropped to sub-lethal amounts, dodder seed will germinate and survive. Repeated applications are normally required.
Contact Tickes: (928) 580-9902 or firstname.lastname@example.org.