June 27, 2007
In this issue
§ Pheromone trap update
§ Squash vine borer and squash bugs
§ Watch for thrips on cabbage
§ Statewide downy mildew sprays recommended
§ Too bad for cucumber growers!
§ Regional Reports
§ Weather
Beth Bishop
Entomology
The numbers of European corn borer moths caught in pheromone
traps were low again last week in most locations except for the site in
European
corn borer moths caught in pheromone traps in
different
|
Location |
Moths per trap |
|
|
1.3 |
|
|
0.0 |
|
|
0.0 |
|
|
0.0 |
|
|
2.0 |
|
|
1.0 |
|
|
0.0 |
|
|
0.7 |
|
|
0.0 |
|
|
34.3 |
Only a few corn earworm moths were caught in pheromone traps. In general, we have not had weather conditions that are conducive to insect migration from the south.
Beth Bishop
Entomology
Squash vine borer adults and squash bugs have been reported
on vine crops in
Growers should scout their pumpkin and squash fields weekly for squash vine borer from late June through early August. Examine the base of vines for evidence of larval feeding (sawdust-like frass near entrance holes) and then split open the stem to confirm the presence of larvae, which suggests more eggs are being laid. Two insecticide sprays, ideally applied to the base of the plants, and timed five to seven days apart, will control newly hatching larvae before they are able to bore into the stem. Consult Bulletin E-312, 2007 Insect, disease and nematode control for commercial vegetables insecticides registered for control squash vine borer on your crop.
Squash bugs are serious pests of pumpkins and squash. Both adults and nymphs feed by inserting their beak and sucking juices from plant tissue. Large populations can cause partial wilting, and later in the season, squash bugs may feed on the fruit, causing them to collapse or become unmarketable. Adults are 0.5 to 0.75 of an inch long, flattened and grayish-brown. Wingless nymphs are similar in appearance to adults, and are whitish when small, with a brown head, and grayish white when larger. Eggs are laid in clusters usually on the underside of leaves and are orange when first laid, but turn bronze-colored before they hatch.
Squash bugs are virtually impossible to control later in the season when nymphs are large and the canopy is dense. The key to preventing squash bug problems is early detection and control of small nymphs. Growers should scout their field regularly for evidence of squash bug adults and eggs. Insecticides may be warranted if squash bugs are causing wilting of young plants (wilting is observed and squash bugs are present on the underside of leaves). Just before flowering, fields should be scouted for egg masses. This is the critical time to control squash bugs. If more than one egg mass per plant is found, an insecticide application is needed.
Beth Bishop
Entomology
Thrips are reported in cabbage fields. Thrips populations can build up rapidly in hot, dry weather. Be aware that the Bt materials (Dipel, etc.) applied for control of “worms” are not effective against thrips. Consult Bulletin E-312, 2007 Insect, disease and nematode control for commercial vegetables insecticides registered for control thrips on cabbage.
Mary Hausbeck
Plant Pathology
Downy mildew fungicide sprays should be applied to all cucumbers in the state immediately! Fungicides should be applied to cucumbers every five to seven days.
Pumpkins, melons, cantaloupes, squash, zucchini and gourds should also be protected with downy mildew fungicides. Fungicides to these crops should be applied every 7 to 10 days.
Table 1. Recommended
products for managing downy mildew on cucumber and all cucurbits.
|
Applied before disease (7-day intervals) |
Applied after disease (5-day intervals) |
|
— Gavel 75WG (5 day PHI) |
— Previcur Flex 6SC (2 day PHI) |
|
— Previcur Flex 6SC (2 day PHI) |
— Ranman 3.6SC (0 day PHI) |
|
— Ranman 3.6SC (0 day PHI) |
— Tanos 50WG (3 day PHI) |
|
— Tanos 50WG (3 day PHI) |
|
|
Alternate products and mix each with either: — Dithane (mancozeb) 3 lb or — Bravo (chlorothalonil) 1.5 pt |
Alternate products and mix each with either: — Dithane (mancozeb) 3 lb or — Bravo (chlorothalonil) 2 pt |
Use fungicides proven to work on cucumbers in
Downy mildew on cucumber was confirmed on June 25 in a
homeowner’s garden in
These cases appear to be the result of relatively new
infections that have become established within the last 7-10 days. A weather
event may be responsible for the nearly simultaneous downy mildew outbreaks in
If you suspect downy mildew please have it confirmed either through my lab (517)355-4576 or through Dr. Jan Byrne at MSU Diagnostics (517)355-3504. To better understand this downy mildew, my laboratory is collecting diseased plants for further analysis. If a sample cannot be sent to the lab, please call and arrangements will be made to pick it up.
Paul Marks and Jennie Stanger
Extension Educators
Late on June 25, Paul Marks and Jennie Stanger visited a
home gardener who felt his cucumbers were showing the same symptoms as last
year when an unprecedented outbreak of downy mildew swept across the county in
midsummer, killing nearly all home garden cucumber plants and many farm field
plantings within several days. Unfortunately, he was correct and this may be
the first confirmed outbreak in
Commercial growers were already taking preventive measures
because the disease had been reported this month in
Paul Marks’ three photos show the yellowish spots first visible on the topside of leaves, the dirty look at the bottom side of those spots from all the tiny black spores forming, and the declining health of an infested plant.
The reason growers must spray often is that the cucumber
plants are quickly forming new leaves, and the reason for rotating chemicals is
that the disease would otherwise develop resistance to one product used all the
time. Furthermore, this disease is so different from the “normal” cucumber
diseases like common powdery mildew, that at least two different fungicides
must be used. It is not economical nor convenient for home gardeners to attempt
chemical control. In fact, it is expensive and difficult for commercial growers
as well. This one disease has potential to ruin the entire pickle industry in
Last year some people blamed the first farm in the county
where the disease was found, thinking that because the cucumber plants on that
farm were early and large due to plastic and row covers, that perhaps the
disease had been brought to that farm on plants from the south. However, this
year, after learning of downy mildew reports from year-round cucumber
production greenhouses in
Home gardeners around
Bill Steenwyk
Conditions have been hot, with most areas receiving no
significant rain for at least eight days.
Celery continues to look good, with early harvests approaching.
Some onion and leek fields have been pressured by thrips.
Cabbage harvest continues, with the crop looking good overall. The success of newer transplants depends on the ability to maintain adequate irrigation.
Irrigated tomatoes, peppers and vine crops appear to be developing well.
Many sweet corn fields look good overall. Stewart’s bacterial wilt is limiting the potential of some fields. One field, otherwise vigorous, shows substantial corn smut tumors in the leaf tissue. No European corn borer moths were found in the three pheromone traps.
Norm Myers
Our area hasn’t seen any rain since last week’s report. Irrigation is once again going at full tilt, especially now that the hot, humid weather has returned. Last week’s rain did make all of our crops jump in height, but are also at the point of needing another rain or un-irrigated crops could begin to go backwards.
There are a couple of growers still picking some fresh asparagus, but in general fields have been let go to fern for the season. Purple spot is a common problem in younger fields, partly I think, because of all of the damage from blown sand that we experienced earlier. I have not seen any final numbers for 2007’s crop, but I am sure it is significantly down from last year.
Carrots benefited greatly from last week’s storm and the cooler weather that followed. Growers are irrigating furiously again, however. Tom-Cast sensors are launched, but haven’t been read yet. Very few aster leafhoppers reported as of yet.
Winter squash and pumpkins are advancing nicely, with no reports of virus yet. However, most of these fields are not irrigated and will begin to suffer drought stress pretty quickly.
Most zucchini fields are now planted. So far, we have had very few pest problems.
In sweet corn, earliest planted fields are in tassel. I only caught two European corn borers and no corn earworm this week.
Snap beans growers have begun planting the late snap bean crop. Where irrigation is not available, the beans are being planted in to dry soil.
Jim Breinling
Rainfall of 0.06 inch on Thursday June 21 is all that was
reported at both the Ludington and Fremont MAWN stations during the past week.
Daytime high temperatures at the Ludington station nearer to Lake Michigan were
generally in the high seventies, while at
Uneven growth can be seen in some carrot fields due to dry conditions and wind damage to foliage. Aster leafhopper counts continue to remain low.
In pepper fields, wind damage has become more evident and in some spots has resulted in plant loss.
Harvest of spinach has started, the warm temperatures and dry conditions have resulted in some acres not being harvested.
Planting of snap bean
acreage will be heavy during the next two weeks. Soil moisture will be needed
in some areas for planting and germination. The European corn borer counts at
the
First planting of sweet
corn in
Plantings of hard winter squash are growing nicely, and some fields are starting to run, in these fields sidedress nitrogen has been applied.
Hannah Stevens
It is precariously
dry in this area, and while drip irrigated vegetable crops are doing well,
those such as sweet corn are showing stress. A humid 94oF yesterday
was the high for the week, but wind is an issue in high evapo-transpiration
rates. I am hoping for a shower today.
In sweet corn, European corn borer flight continues to be troublingly high with an
average of 34 moths per trap and reports of heavy infestation of small worms in
the emerging tassels. The plants are under drought stress, and this combination
with the high temperatures are not an ideal spray situation. Otherwise the crop
is making rapid progress in this heat.
In winter squash, Phytophthora blight has been confirmed in a field on plastic and drip
irrigation. Isolated plants are affected.
Summer squash, including zucchini and yellow squash, are
approaching harvestable yield. Several plants exhibiting virus symptoms have
been seen. (see photo)
Muskmelons and
watermelon fruit are sizing at a
remarkable rate, from walnut size to football size in a week.
Tomatoes are setting fruit, and the first set appears
to be of good quality. A case of distorted foliage was traceable to glyphosate
drift. (see photo)
New potatoes are now available at local farmers’ markets. (see photo)
The lettuce crop, both wholesale and retail, continues to be harvested and is of good quality and yield. As of last week, aster leafhopper pressure was low and aster yellows not a problem,
The carrot and onion crop on muck soils was in excellent shape last week, but rain is needed.
Paul Marks
Hot and dry has been our situation for the last seven days in our area. Most farms are in need of rain and irrigation systems are all running. Estimated potential evapotranspiration for this last week has been more normal, at approximately one quarter of an inch per day, allowing irrigation to at least catch up with the need on most farms.
Sweet corn is in full silk in early fields, and at first harvest in smaller isolated plantings that were under tunnels. Corn borer traps this week averaged less than one moth per trap for the second week in a row with low moth pressure. However, even fields that were treated regularly during the higher moth flights three and four weeks ago have some worms present.
Tomatoes have made very good growth during this warm weather and appear to be very disease free at this point. Early fruits in market tomatoes also appear to be of good quality, although first harvest is a week or so away in earliest plantings.
Cucumbers in our area are now showing the first indications of downy mildew with confirmations in both one home garden and one commercial field. These two infestations are more than 15 miles apart! Neither of these infested plantings had been protected with recommended fungicides. I have not seen any symptoms of this disease in any treated fields.
Larger vine crops such as hard squash and pumpkins are now beginning to vine with some fields having very poor stands as a result of our hard rainfall the week after they were planted. Some replanting has been done this last week. This week, I have seen both squash vine borer moths and squash bug egg masses in pumpkin fields.
Potatoes continue to look good, although stressed for moisture in a number of fields at a poor time (tuber bulking), where irrigation has not been able to keep up with need. Leafhoppers continue to pressure this crop, and while controlled with insecticides, reinfest some fields within two weeks. No disease found in this crop so far this season.
Cabbage harvest is now rolling along at full steam. I have seen several fields this week with thrip feeding just below the outer wrapper leaves. Other worms have not been a problem in our area.
Jeff
Andresen
Agricultural Meteorology
Geography
Following another entire week without significant rain, a
weak- and slow-moving cool front will move west to east across
As mentioned here last week, medium range forecast guidance
is suggesting the formation of an upper air trough across the eastern
On the brighter side, temperatures are expected to be cooler, which should reduce water use rates. Mean temperatures across the state are forecast to remain at near normal levels statewide during the 6-10 day time frame, while below normal temperatures are expected state- and region-wide during the 8-14 day period.
Earlier this year, sea surface temperatures in the equatorial Pacific region were falling and the development of an El Niño event looked possible. That surface temperatures trend unexpectedly stabilized during the spring season and has remained steady since, reducing the chance of an El Niño anytime soon. ENSO factors thus play little if any role in the new series of NOAA long lead outlooks for the upcoming months.
For the month of July, the outlooks are directionless for