April 18, 2007
In this issue
§ Corn flea beetle, sweet corn and Stewart’s wilt
§ Honey bee colony collapse disorder and vegetable growers
§ Holding the line on fertilizer costs
§ New herbicide labels for 2007
§ New formulation of Kocide® 3000 available for 2007
§ Enviro-weather is geared-up for the 2007 growing season
§
§ Weather news
As we put the finishing touches on this issue, it appears we
have a normal spring in
We recently said good-bye to assistant editor Rebecca Lamb. She has been a reliable and capable
hand in production of this newsletter over the past six years and we will miss
her contributions here at IPM Communications. Rebecca left for new challenges
as a graphic artist for a
Next issue – May 2
If you have suggestions for our newsletters, please feel free to contact me at (517) 353-4951 or catalert@msu.edu. Internet readers can also sign up to receive a brief email when we post new issues on the Internet. See this site for details: http://ipm.msu.edu/email-veg.htm – Joy Landis, editor.
The corn flea beetle is a small, black beetle that feeds as an adult on a variety of grasses, including sweet corn. (view images) Feeding by corn flea beetle produces linear scars along the leaf. Usually corn flea beetles do not directly damage corn. They do, however, vector the bacterial disease, Stewart’s wilt. This disease can cause wilting, stunting, and reduced stand and yield in sweet corn.
The Stewart’s wilt bacterium lives in plants and in the gut of flea beetle. Flea beetles acquire the disease when feeding on a diseased plant. Infected flea beetles, in turn, infect new plants by feeding on them.
Corn flea beetles survive the winter as adults hidden among leaf litter and debris in ditch banks, hedgerows and other areas bordering fields. Some beetles that emerge in the spring may carry the Stewart’s wilt bacterium in their guts, having become infected the previous season. Wild grasses may also harbor Stewart’s wilt, but whether they are an overwintering source of the pathogen, is not yet known..
In
Given this, sweet corn in south and central
If growers are planting a susceptible variety in an area that is prone to Stewart’s wilt, insecticides may be used to control flea beetles. Sweet corn plants are most vulnerable to Stewart’s wilt when they are small. In general, the smaller the plant, the greater the impact Stewart’s wilt has. Control of corn flea beetle is only needed until the 7-leaf stage. The most effective option is to purchase seed that has been treated with systemic insecticides (Gaucho, Cruiser, or Poncho). These insecticides are effective against corn flea beetles and the protection lasts until the 5th true leaf stage. Several soil insecticides are also effective against corn flea beetle feeding. Of these, Furadan 4F gives the best control. Alternatively, Counter 15G or Thimet 20 G may be used. These products will give control for two to four weeks.
If growers are planting more tolerant varieties, or if they are growing corn in areas that do not usually experience problems with Stewart’s wilt, scouting fields for corn flea beetles and feeding damage and applying a foliar insecticide when needed may be the best option. Field should be scouted two to three times per week, especially near the field edges, from germination until the 7-leaf stage. Flea beetles are best observed on a sunny day with little wind (they hide in the corn plant if it is cloudy, cold or windy). The treatment threshold is 6 beetles per 100 plants for susceptible varieties and 2 beetles per plant in combination with feeding damage on 25 percent of plants for resistant varieties. A number of foliar insecticides are registered and are effective against corn flea beetles (see Bulletin E-312: 2007 Insect, Disease and Nematode Control for Commercial Vegetables). Keep in mind, however, that the corn plant is growing rapidly early in the season and any new growth since the last application is not protected. In addition, flea beetles are very mobile and may move into the field from the borders after the application and feed on the unprotected foliage.
By time the corn plant reaches the 7-leaf stage corn flea beetle control is no longer needed. Although flea beetles may still feed on the corn and may still infect it with Stewart’s wilt, the plant is large enough to tolerate the infection without any damage to yield or quality.
If you have been listening to the radio or reading papers the last few weeks, chances are that you have already heard about the alarming honey bee die-offs around the country. The phenomenon is officially named “colony collapse disorder” (CCD). This disorder has the media all excited because it is large in scale (25 states are affected), came in quick (colonies that were fine in August/September became collapsed around October/November), and hit people hard (many beekeepers with hundreds to thousands of colonies are losing 50-90 percent of their colonies). The worst of all, we do not yet know what causes it.
The symptom seems to be that bees simply disappear. That is why initially peopled called it the disappearing disease (or fall dwindle disease). A colony with 40,000 bees in the fall, apparently healthy with lots of honey and pollen, suddenly has nothing or a handful of bees with a queen left. Very few dead bees are found inside the hive or near the entrance. Strangely, wax moths, small hive beetles and robbing bees are slow in moving into such newly abandoned colonies – typically these things do not happen until two to three weeks later, while normally they move into defenseless colonies right away. Several possible causes come to mind. When tracheal mites (Acarapis woodi) first showed up in North American (circa 1983), we had bees disappearing. The disappearing mostly happened during the overwintering process – colonies had small clusters or no bees in the spring because bees with their trachea plugged with mites could not make it back to the colony after defecation flights or they simply flew out to die in late fall.
A new species of
nosema (Nosema ceranae, so named
because it was discovered first in the Asian honey bees, Apis cerana) also showed up in the European bees (Apis mellifera, the only species we have
in North America and Europe) in
Another concern is all the chemicals we have been throwing into bee colonies, which conceivably can weaken the immune system of honey bees or affect their learning and orientation. A few years ago, French beekeepers suspected that their “Mad Bee Disease,” where bees got confused and could not return home successfully, was related to the use of an insecticide called Gaucho (actively ingredient: imidicloprid).
Unfortunately, all these factors (tracheal mites, nosema
disease and pesticide use) are unlikely to be the causes of CCD. Scientists
from
Editor’s note: Get more bee information from Dr. Huang’s web site at: http://bees.msu.edu/.
The expected increase in corn acreage has driven the price of nitrogen (N) fertilizers to all-time highs. The cost of nitrogen from urea and urea-ammonium nitrate (28 % N solution) is near 50 cents per pound of N (urea at $460/ton, and UAN at $280/ton). And the price is even higher for some of the other nitrogen materials, such as calcium nitrate. Hence, it is important to manage N inputs as effectively as possible to minimize loss and maximize plant uptake. During the first 4 to 5 weeks after seeding or transplanting, the requirement for N of vegetable crops is relatively low. Where possible, apply N, P and some K in a band near the transplant or seeded row. This will increase early utilization of these nutrients compared to broadcast incorporation. By banding fertilizer the early N rate may be reduced by 25 percent, e.g. 30 compared to 40 lbs N/acre. Then, make subsequent top or sidedress N applications as needed. Providing the N at the time when the crop has a greater requirement will increase plant uptake and minimize the potential for loss by leaching or denitrification if a heavy rainfall event should occur. A presidedress soil nitrogen test (PSNT) can be very helpful in applying the correct amount of N. The PSNT run on soil samples collected prior to sidedressing can indicate how much N is available in the soil, and the amount to apply can be adjusted accordingly. This can be especially important where cover crops, compost or animal manures have been incorporated.
Phosphate and potash prices are near record highs as well. Vegetable crops do require higher levels of available phosphorus than field crops, but the phosphorus level has been built up over time in many soils used for vegetable production. In mineral soils with a P soil test between 40 and 70 ppm, applying 30 to 40 lbs P2O5/ acre in a band is adequate and actually will equal crop removal for many vegetable crops.
The available potassium levels in the loam and sandy soils used for vegetable production tend to be less than adequate. Recommended amounts of K2O usually include an amount for building up the soil level plus an amount equal to removal in the harvested portion of the crop (maintenance amount). Where the budget for inputs is tight, applying only the maintenance amount of K2O will be adequate for production of top yields, unless the K soil test is less than 80 ppm in sandy soils or less than 100 ppm in loam soils. In muck soils, using only maintenance amounts is adequate as long as the soil test K value is above 220 ppm.
Soil testing is the primary key to long term cost effective
nutrient management. In vegetable crop production it is important to soil test
at least every two years, if not annually. It is very important to monitor the
soil pH on a regular basis. Many times where crop growth problems occur, it is
related to the soil being too acid. Fairly intense sampling can be beneficial
in vegetable production. Collect soil samples according to variations in
fields. This may mean delineating sampling zones that may only be 5 to 6 acres
or less in size in some fields. During the growing season, observe the crop and
note those areas where crop growth is not as good as the rest of the field. Soil
sample these areas separate from the whole field. More information on the
nutrient requirements of vegetable crops can be found in MSU Extension Bulletin
E-2934, Nutrient recommendations for
vegetable crops in
Several new herbicide labels have been issued for vegetables
in
A Section 18 Emergency Exemption has been issued for use of Spartan
4L on strawberries in
A Section 24c label (SLN) has been issued for use of Kerb 50W on lettuce and rhubarb. For lettuce, Kerb may be used at a rate of 8-12 lb of product/acre (4-6 lb active ingredient). At these rates on muck soil, Kerb will give about 4 weeks control of most broadleaves and grasses. It should be applied soon after seeding. The fields normally will require cultivation or hand weeding to maintain sufficient weed control until harvest. There is a 55 day preharvest interval.
For rhubarb, apply 2-4 lb of product per acre to rhubarb in the fall for suppression of quackgrass, annual grasses and some broadleaves the next spring. It also may be applied early in the spring before rhubarb begins to grow. There is a 38 day preharvest interval.
Nortron is now labeled for garden beets, onions, garlic and shallots. On beets, 60 fl oz (3.75 pt) may be applied pre-emergence. It may be applied post-emergence at 5.25 fl oz on 2-4 leaf beets, and at 10.5 fl oz on 6-8 leaf beets. Nortron will control many broadleaf weeds.
On onions, garlic and shallot, apply 16-32 fl oz pre-emergence or 16 fl oz post-emergence. Up to four post-emergence applications may be applied. There is a 30 day preharvest interval. Nortron will improve control of common chickweed, common lambsquarters, redroot pigweed and ladysthumb smartweed. It also will help suppress yellow nutsedge.
We anticipate a Dual Magnum label for pumpkins and possibly winter squash for 2007, and also a Prowl H2O label for carrots.
DuPont Crop Protection has introduced a new formulation of Kocide 3000 for the 2007 season. This formulation has a finer, more consistent copper hydroxide grind than previous Kocide formulations and some competitive copper products. Kocide 3000 has more copper ions available to provide disease control at a lower rate. The environmental benefit is less metallic copper applied per acre.
Improvements made with Kocide® 3000 include:
§ More available copper ions per pound metallic copper.
§ Improved worker safety including signal word 'caution', no PPE eyewear required, no early entry eyewear required, and there is no 7 day eye flush container and oral warning.
§ Improved handling characteristics including quicker dispersion, cleaner screens, low foaming.
§ Lower use rates, 2/3x Kocide® 2000 use rate.
§ Kocide® 2000 and Kocide® 3000 each received the OMRI approval to use on organically grown crops.
Kocide products have been used very successfully against many bacteria and diseases on fruit and vegetables. This preventative copper fungicide has also demonstrated very good activity against Septoria and powdery mildew in wheat to protect early plant health.
Ready for its second season, the Enviro-weather website is
all set to be your source for agricultural weather and weather-based plant and
pest management decision making tools. Just visit http://www.enviroweather.msu.edu and you will have access to
information and management products from 50 weather stations across
Weather information such as National Weather Service local forecasts and real time radar, overnight temperatures and weather summaries, including temperature, degree days and rainfall can be accessed by clicking on the weather station of interest to you. In addition, you can get summaries and decision making products specific for your favorite crop or area of interest by choosing from links to forestry and Christmas trees, fruit, potato or turfgrass. In addition, plans are underway for a vegetable crops section on Enviro-weather.
Enviro-weather invites self-identified work groups to provide direction on tailoring the information system. These workgroups typically include web site users such as farmers, resource managers and consultants along with MSU specialists and Extension educators. They are essential in identifying needs and priorities:
§ Are relevant weather-driven models/information available for integration into the system?
§ Which educational, extension and research resources should be linked to the system?
§ What supplemental external resources for research, partnerships, funding are needed?
§ Are additional weather stations needed and if so, how will they be supported?
A new workgroup is being formed to answer these questions relating to vegetable crops. If you have input pertaining to the items above or would like to be part of the workgroup contact Mark Trent at trentm@msu.edu or (517) 432-6520.
For easy access to Enviro-weather’s home page just type “enviro-weather” in the Google search engine and click “I’m Feeling Lucky.” In most other search engines Enviro-weather will be at the top of the results list. Watch future editions of Vegetable Crop Alert for more Enviro-weather tips.
Temperatures have generally been below normal since April 1. High temperatures have ranged from 27 to 72ºF and lows from 21 to 46ºF. Soil temperatures are currently in the mid 40s. Higher temperatures occurred early in the month with freezing temperatures beginning April 4. We have had 12 nights so far in April where the temperature has dropped below freezing. We have had 1.14 inches of precipitation since April 1.
Asparagus was coming up at the time of freezing temperatures beginning April 4. Cold temperatures have kept the plants dormant since that time.
Growers are marking out and working the soil getting it ready for plastic, but so far no plastic has been laid. Cool temperatures continue to delay activity.
There are many significant off-season weather developments to report as we begin this growing season. Among them:
§ An abnormally cold, wet October,
§ Record or near record warmth for much of November through early January,
§ Winterlike conditions for much of February,
§ Unseasonably mild temperatures during late March and early April, and
§ Abnormally cold, winter-like weather since the first week of April.
From an agronomic standpoint, the most significant would probably include the above normal precipitation totals, relatively mild soil temperatures due to abnormal warmth in December and January and later to extensive snowcover in February and early March, and to cold injury of overwintering crops associated with last week=s spell of late winter weather.
The mild overwinter soil temperatures may lead to some extra
insect and possibly disease pressure to deal with this year (e.g. flea beetle
and Stewart=s wilt). There
is good and bad new regarding the above normal moisture. The bad news is that
it will likely lead to some delays in early spring fieldwork during the next
few weeks. The good (and probably best) news is that much of the state will
enter the growing season with a rooting zone with a full or nearly full soil
moisture profile, which may become indispensable later in the season should any
prolonged dryness develop (not expected at this point). The latest Palmer
Drought Severity Index values for the state categorize all of the Lower
Peninsula as unusually to extremely moist, with near normal values for the
Looking at the current weather situation, there is reason to
believe the unusually cold weather pattern of the past one to two weeks will
soon be coming to an end (at least temporarily). On Wednesday (April 18), an
upper air disturbance combined with residual moisture from the
A weather system approaching from the west will bring the
next chance for precipitation in the form of showers and thunderstorms by as
early as late Sunday or more likely next Monday. A cooler and more unsettled
weather pattern is likely to set up once again across the region by the middle
of next week. Current medium‑range forecast guidance suggests the
formation of upper air troughing across western sections of North America,
which would lead to more springlike conditions here in
The official NOAA 6-10
day and 8-14 day outlooks
(covering April 23-27 and April 25 through May 1) both call for precipitation
to increase to above normal levels once again statewide. Mean temperatures are
forecast to remain at near normal levels during the 6-10 day period, and range
from near normal in northwestern sections of the state to above normal levels
in the southeast during the 8-14 day time frame.
During the past couple of months, the El Nino/warm water
conditions of last fall have rapidly dissipated so that sea surface
temperatures in the central equatorial Pacific region haven fallen back to near
normal or even slightly cooler than normal levels. With this reversal there is
now a chance for the development of a La Nina or cool ENSO event within the
upcoming months. Given the current near neutral conditions, however, potential
ENSO-associated weather anomalies across North America during the next few
months will likely be limited to southern sections of the