FIELDAND
FORAGE
CROPS
FIELD
The information and recommendations in this newsletter are applicable to
North Carolina and may not apply in other areas.
Across much of our state's cotton acreage, the thrips and aphid situation has improved, especially where moisture is adequate to good. However, most of the cotton is 1.5 to 3 weeks behind schedule and can not afford a further maturity delay, from insects or other factors. Therefore, many insect treatment decisions must still be in favor of protection.
Natural control (predators,
parasites and fungi, for the most part)
remains our most effective means of managing cotton aphids, and
thrips populations in some areas (e.g., Scotland, Hoke and Robeson
counties), seem to be declining. In a recent (June 18-20) survey
of many of our independent crop consultants working on cotton, it
was discovered that there was very few fields with high or even
moderate aphid levels, although a few fields with dense aphid
colonies were reported scattered throughout our northern counties.
Budworms just now appear to making a late appearance in the
southern part of South Carolina, and populations on tobacco in
North Carolina, thus far, seem to be light.
Thrips remain our primary headache, with perhaps as many as two-
thirds of our cotton acreage still susceptible to this pest. If
the criteria for thrips treatment have been met (newly-unfolding
small leaves crinkled and/or buds twisted and brown or black and
either adult and/or immature thrips found), treatment is likely in
order. Cotton plants past the 6-leaf stage
are likely out of
danger, if moisture is adequate. However, treatment of cotton at
this stage should be considered if dry conditions prevail and
thrips symptoms are present, because 6 to 7-leaf cotton is still
significantly behind schedule.
Although aphids have generally declined during the past week and are at present a potential problem in a very low percentage of cotton fields, those fields with high populations present a treatment dilemma. A significant portion of the cotton aphid population is likely resistant to organophosphate insecticides and the synthetic pyrethroid Capture. Provado may be worth considering, as it has provided good control of cotton aphids under growing conditions in Florida, Georgia, South Carolina and in a few fields in North Carolina in recent weeks. We will have to see, however, if aphids rebound a week to 10 days following treatment. Remember the 12-month plant back restrictions for corn, soybeans and peanuts with Provado, however. Growers are okay with a rotation to tobacco, cotton or wheat. Natural control will likely be the most effective aphid "option" in the vast majority of fields with moderate to high populations. Aphid mummies have begun to occur with greater frequency, and the parasitic fungus has mercifully made an early appearance also, providing the potential for significant help. However, much about the present early cotton aphid situation is still a matter of speculation with the early appearance of cotton aphids at these numbers and the almost unprecedented late cotton crop. We will learn much more our cotton aphid outlook this coming week with results from replicated trials and further observations.
Partial results from an aphid test evaluated on June 20 are
presented in the following table:
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Rate Number of plants Number
(lbs. with aphid counts in Number of of other
a.i. the following ranges mummified beneficial
per ************************ colonies arthropods
Product acre) 0 1-10 11-50 51+ (40 plants) (40 plants)
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Capture 2E 0.04 0 1 5 34 40 1
Cygon 4E 0.25 0 1 14 25 39 1
Provado 1.6F 0.047 1 13 19 7 24 # 2
Furadan 4F 0.25 4 20 14 2 25 # 0
Check ## 0 0 2 38 40 3
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# the lower numbers of mummified colonies are the result of good control
## aphid numbers in adjacent cotton field similar to test check
Control of aphids (or reduction in mummified colonies) by Capture and Cygon was very poor. Plants in these treatments and the check appeared to be more stressed than those in the Furadan and Provado- treated plots. Control with Provado at this high rate (3.75 ounces per acre) was probably acceptable, as the 7 of 40 plants had just over 50 aphids per plant and many of the 38 plants in the check had 100 to perhaps 300 aphids per plant. Parasitized aphids (mummies) were plentiful, thought it is difficult to determine if this will be enough to control this particular population (the worst I have seen). Given the very late crop, the grower's cotton field may be in need of treatment. An additional evaluation will be taken.
Furadan is not presently labeled on cotton in North Carolina. A Section 18 exemption is under consideration for this product; however, there are also some potential safety considerations for Furadan 4F use on cotton.
Provado at the 2.0 ounces per acre rate with an organosilicone
surfactant should provide adequate to good control of up to
moderate populations of aphids.
Two-spotted spider mites are still remaining in a few cotton
fields, mostly in the northern half of the state. In areas which
have received a good stress-reducing rainfall, these mites can be
generally expected to decline, especially if the parasitic fungus
of mites makes an early appearance. As was mentioned in last
week's North Carolina Pest News, Comite and Kelthane are probably
the materials of choice for treatment of spider mites. Sometimes
a second treatment may be required. Prior to possible treatment,
a yellowing of lower leaves in at least scattered portions of the
field (including the interior) along with some defoliation should
be confirmed.
With budworms recently occurring in South Carolina (June 17), their
appearance in southern North Carolina might reasonably be expected
during the week of June 23-27 (perhaps a little later). So far,
this has not been a large flight to our south. Spot scouting for
budworms in terminals and squares should begin in the coming week.
The time of year is approaching when many growers begin considering the application of an insecticide for southern corn rootworm control. The underground nature of this pest, as well as the means of control, creates a situation where growers must rely upon preventive insecticide treatments. Our decision to treat is based upon soil type and past history of rootworm problems.
Rootworms generally cause more damage to smaller, immature pods than to the larger ones. Since the rootworms occur about the same time each year, the determining factors on whether or not they will cause a yield loss are the abundance of the rootworms and the maturity of the crop. Most peanuts were planted late this year and all peanuts got off to a slow start. This increases the likelihood that when rootworms attack peanuts in August, the crop will be relatively immature. Therefore, the likelihood of yield loss from rootworms is greater than normal. Only the number of rootworm beetles and the weather in late July and August will determine the actual number of rootworms. In other words, the threat of rootworms is unknown at this time, but the risk of yield loss should rootworms occur may well be greater than normal due to the late crop.
The mild winter appears to have been favorable to overwintering
spider mites. They are quite abundant in many locations and if we
have dry weather in July, be prepared to scout for this pest.
Web page last updated on June 23, 1997 by Stephen J. Toth, Jr..
