ISSUE 8 June 22, 2006
BEGIN SCOUTING FOR SOYBEAN APHIDS
The first soybean aphid was detected on June 15, 2006 in northeastern North Dakota. Low levels of soybean aphids have been observed in soybean fields in the southeast (Cass, Richland, Traill counties), and northeast regions (Walsh, Grand Forks, and Nelson counties) of North Dakota from June 15-20, 2006. Average numbers of aphids are very low about <5 aphids per plant with a high of 40 aphids per plant. Winged aphids were present. Crop stages of soybeans are still in the early vegetative stages (VC to V3) crop stages. The Multicolored Asian lady beetle (Harmonia axyridis), a predator of soybean aphids, was also observed in soybean fields.
Begin scouting fields at the V3 to V4 stage to determine if soybean aphids are present in fields. Check numerous locations within a field for aphids as their distribution is often spotty throughout a field. No treatment is recommended at this time and is discouraged so insecticides do not reduce the presence of predators and parasites. Early detection of soybean aphids does not necessarily mean that we will have high populations of aphids this year. It does mean that we need to be vigilant on scouting for soybean aphids. Stay tune for more updates and information on treatment thresholds.
GRASSHOPPER ACTIVITY INCREASING
Continue monitoring the field edges and entire fields of agricultural crops for young grasshopper nymphs. There has been a few reports of increased grasshopper hatching / activity in north central region. Grasshoppers are more easily and economically controlled while they are in the nymph stage and still within hatching sites, such as roadsides and fencerows. The warm spring is causing an earlier hatch and more rapid development. The rainfall has been sporadic throughout North Dakota. Under these hot dry conditions, a small grasshopper can do as much damage as a large grasshopper under cool, wet conditions.
CANOLA INSECT PEST TRAP NETWORK
A trap network is being coordinated through the NDSU IPM Survey Program for diamondback moth and bertha armyworm in canola this year. Trap catches for diamondback moth are VERY LOW and pose NO THREAT to canola crop so far. The trap catches range from 0 to 18 moths per trap week for this past week throughout the southwest, north central and northeast regions of North Dakota. No report for bertha armyworm.
DEGREE DAYS FOR COLLECTING LEAFY SPURGE FLEA BEETLESThere has been several questions about how many degree days are required for collecting leafy spurge flea beetles. The accumulated growing degree days (AGDD) for sunflower (base of 44F) can be used as a guide to determine when to begin scouting for adult flea beetles. Begin scouting for adult flea beetles when the AGDD approaches 1,000. Likewise, the flea beetle population and egg laying by females begins to decline when the AGDD reaches 1,600 or more.
Collect flea beetles between 1,200 and the 1,600 AGDD. Peak emergence of Aphthona spp. flea beetles also corresponds to the flowering of the prairie wild rose and the ripening of garden strawberries in North Dakota. See current map of AGDD in North Dakota. Use the sunflower degree days/growth stage application in NDAWN and enter "2006-03-01" for planting date and select "degree day" for map type.
WHITE HEADS IN WHEAT - WHEAT STEM MAGGOT
White heads have been reported in winter wheat in southwest regions of North Dakota. This is from feeding injury caused by the larvae of wheat stem maggot (a fly). The wheat stem maggot damage becomes evident after flowering when seeds begin to develop. Normally the first indication of its presence is the dying and whitening of the wheat heads (see photo) and upper internodes while the lower stem and leaves remain green. A single maggot will be found inside the straw just above the last node. The plant stem pulls out very easily and if larvae are not found, the stem is usually cut off. The presence of white heads alone is not always an accurate assessment of damage. The maggots can also infest young tillers prior to the boot stage causing the affected tiller to abort. These aborted tillers can account for an unseen loss in yield. Little is known about this insect pest, and no chemical controls are recommended. Two diseases can also cause white heads are scab and root rot.