By Nick McGhee
I have been in several wheat fields in the last couple days and most of them have moved into the jointing growth phase. Once the wheat reaches this growth stage, it has gotten too mature for most herbicides and has also passed the optimum time for applying topdress nitrogen. Any wheat that has not reached the jointing growth phase should be there quickly.
Also, I am beginning to see a few aphids in the wheat fields but nothing near treatable levels. Below is a picture of some aphids on a wheat leaf:
Here is an excerpt from the 2012-2013 UGA Wheat Production Guide regarding aphids in wheat:
Aphids are small, soft-bodied insects that can be found in wheat anytime during the growing season. The most common aphids found on wheat are the bird cherry-oat aphid, rice root aphid, greenbug, corn leaf aphid, and English grain aphid. The first four occur mostly in the fall and winter. Only the greenbug causes direct feeding damage that appears speckled brown and discolored with some leaf curling. The other aphids usually do not cause obvious feeding damage. The English grain aphid is mainly present in the spring and can reach large numbers on flag leaves and developing grain heads. Damage from this pest can reduce kernel size and lower grain test weight. For the most part, beneficial insects such as lady beetles are not active during the winter and only exert some control over aphids during the spring in wheat.
Aphids also vector a viral disease named barley yellow dwarf (BYD) and a related disease called cereal yellow dwarf. Wheat and barley can be severely damaged, but oats are most susceptible to this disease. BYD is present in most fields in most years throughout Georgia. Yield losses of 5-15% are common but losses can exceed 30% during severe epidemics. Infection can occur from seedling emergence through heading, but yield loss is greatest when plants are infected as seedlings in the fall. Although all aphids can potentially transmit certain strains of the virus, infections in the Southeast are mostly associated with infestations of bird cherry-oat aphid and rice root aphid. Planting date is the single most important management practice, with early plantings generally have greater aphid numbers and greater BYD incidence than late plantings.
To sample aphids, inspect plants in 12 inches of row in fall and 6 inches of row in winter. In spring, inspect 10 grain heads (+ flag leaf) per sample. Count all aphids on both the flag leaf and head for making control decisions. Sample plants at 8 to 16 locations per field. Treat when populations reach or exceed the following thresholds:
Seedlings: 1 bird cherry-oat aphids per row foot, or 10 greenbugs per row foot.
2 or more tillers per plant: 6 aphids per row foot.
Stem elongation to just before flag leaf emergence: 2 aphids per stem.
Flag leaf emergence: 5 aphids per flag leaf.
Heading emergence to early dough stage: 10 aphids per head.
Do not treat for aphids after mid-dough stage.
Source : uga.edu