July 26, 2006
In this issue
§
Important update as of July 28
Downy mildew on cukes widespread in Michigan – other crops now infected
§ European corn borer and corn earworm update
§ Aster leafhoppers and aster yellows numbers increasing
§ Regional reports
§ Weather news
All cucumbers in the state are now at a VERY HIGH RISK for downy mildew. Spray programs for cucumbers must be tight and not exceed a five-day application interval. The recommended fungicide program remains unchanged:
Apply: Previcur Flex (1.2 pint) + Bravo (or Mancozeb or Maneb)
Alternate with: Tanos 50DF (8 oz.) + Mancozeb (or Maneb or Bravo)
Remember the pre-harvest intervals (PHI) for these products:
Tanos – 3 days PHI
Previcur Flex – 2 days PHI
Bravo – 0 days PHI
Mancozeb, Maneb – 5 days PHI
All other cucurbits including cantaloupe, hard squash, zucchini, and pumpkins are now at HIGH RISK for downy mildew. I recommend that the fungicide program listed above be applied at five to seven-day intervals. (Please note that mancozeb is not registered on pumpkins but maneb may be used.). In Michigan, downy mildew has been confirmed on cantaloupe in Lenawee County. Hard squash in the Tuscola County area also have downy mildew. Ohio State has reported downy mildew on pumpkin, hard squash, cantaloupe and summer squash. New Jersey has reported downy mildew on pumpkin.
Downy mildew is becoming widespread on cucumbers in Michigan with several counties experiencing significant outbreaks. Just this week, six new Michigan counties have been confirmed including the eastern and western regions of the state (see map). In these regions, several large fields are infected. The infections appear to be fairly new. Although the infections apparently occurred recently, the amount of spores being produced on the undersides of the leaves is especially high.
The weather is not helping us keep the downy mildew contained. The overcast, wet and humid weather favors this disease and promotes massive production of spores that can be moved to new growing areas. Compared to last year, the weather this year is much more favorable for downy mildew. Not only is downy mildew here earlier this year than last year, but the weather is much more favorable this year than last. I think a perfect downy mildew storm is brewing.
Are the spore traps working?
The spore traps are best suited to monitor the spore load in a field that is already infected. Given the nature of the spore trapping, there is always a 7-day lag period until the spore reel is retrieved from the field and then additional time is needed to process the tapes and count the spores. Currently, the spore trap in Monroe is in an infected cucumber field. In the other counties, the spore traps are in fields that currently do not have downy mildew. I’m still in the research mode with these spore traps and it’s quite possible that they cannot be used for early detection (see accompanying table).
Please remain vigilant and continue to look for any downy mildew symptoms on all cucurbit crops (see pictures). Each day can bring a report of a new outbreak. All samples must be confirmed by my lab. This will keep false reports to a minimum. My lab (517-355-4576) and Diagnostic Services (517-355-4536) on campus are available to look at any potential downy mildew samples. I can be reached via cell phone at 517-927-4532.
Table 1. Spore trap daily totals (counts/m 3/day) by location.Date July |
Michigan counties |
||||||
Allegan |
Bay |
Monroe |
Saginaw |
St. Joseph |
Van Buren |
||
1 |
0 |
0 | 10 |
*52 |
12 |
7 |
3 |
2 |
2 |
0 | 8 |
115 |
8 |
2 |
3 |
3 |
0 |
0 | 5 |
8,933 |
32 |
0 |
2 |
4 |
2 |
0 | 8 |
4,345 |
12 |
0 |
15 |
5 |
– |
0 | 2 |
2,448 |
3 |
0 |
5 |
6 |
– |
0 | 2 |
1,045 |
8 |
5 |
30 |
7 |
0 |
0 | 5 |
*1,557 |
2 |
13 |
2 |
8 |
2 |
0 | 8 |
6,268 |
8 |
20 |
20 |
9 |
5 |
0 | 5 |
*122 |
3 |
0 |
7 |
10 |
3 |
0 | 0 |
*93 |
5 |
3 |
5 |
11 |
2 |
0 | 13 |
3,970 |
5 |
0 |
2 |
12 |
2 |
0 | 2 |
48,878 |
5 |
5 |
13 |
13 |
12 |
0 | 23 |
48,230 |
7 |
18 |
30 |
14 |
12 |
0 | 13 |
2,162 |
2 |
3 |
5 |
15 |
3 |
0 | 2 |
52,127 |
5 |
12 |
30 |
16 |
8 |
0 | 2 |
14,185 |
0 |
22 |
63 |
17 |
3 |
0 | 3 |
7,637 |
0 |
7 |
53 |
18 |
2 |
0 | ** |
2,410 |
2 |
2 |
37 |
19 |
13 |
0 | ** |
*62,013 |
** |
** |
** |
20 |
3 |
0 | ** |
51,098 |
** |
** |
** |
21 |
47 |
0 | ** |
*53,398 |
** |
** |
** |
22 |
108 |
0 | ** |
…85 |
** |
** |
** |
23 |
** |
0 | ** |
197 |
** |
** |
** |
24 |
** |
0 | ** |
** |
** |
** |
** |
NOTE: Check my web site for updates to this table. (http://www.plantpathology.msu.edu/labs/hausbeck/hausbeck.htm)
Degree day accumulations throughout most of Lower Michigan are at or near the threshold for second flight of European corn borer moths. (view photos) Few moths were caught in pheromone traps during the week of July 18-25, but numbers could increase significantly in the next week, especially with the projected warmer temperatures.
Growers with snap beans or peppers with fruit or sweet corn at tassel and beyond should treat their crops to prevent infestation. If high numbers of moths are flying or temperatures are high, spray intervals should be shortened to ensure that all plant tissue is covered when young larvae hatch (and are vulnerable to insecticides). After larvae bore into plants, they are protected from insecticides. The exception is the insecticide, acephate (Orthene), which is systemic and is registered for use on snap beans and peppers only (not sweet corn). Since acephate is limited to two applications per year, these should be saved for peak European corn borer flight periods. For insecticides registered to control European corn borer see Bulletin E-312, 2006 Insect, Disease and Nematode Control for Commercial Vegetables. This bulletin can be viewed at http://veginfo.msu.edu.
A few corn earworm moths (view photo) are being caught in pheromone traps. Presently, only low numbers of moths are present. This could change if weather fronts bring adults from more southern locations into the state. August is typically the month when we start to see corn earworm in Michigan, although the numbers and timing can vary. Corn in the green silk stage is most attractive for corn earworm egg laying. Most insecticides applied to control European corn borer will also protect against corn earworm as long as the silks are thoroughly covered. Foliar Bt sprays are generally not effective against corn earworm, since larvae do little feeding before entering the ear (and Bt insecticides must be consumed to be effective).
Aster leafhopper numbers have increased in many carrot and celery fields throughout Michigan. The percentage of aster leafhoppers infected with aster yellows varies between < 1% to 5.6%, depending on location. The table below shows the latest test results from Diagnostic Services and associated treatment thresholds.
|
Date |
Site |
Crop |
% Infectivity |
Treatment Threshold (ALH per 100 sweeps) |
|
July 11 |
Oceana County |
Carrots |
5.6% |
8-10 (carrots) |
|
July 12 |
Mason County |
Carrots |
5.6% |
8-10 (carrots) |
|
July 17 |
Newaygo County |
Carrots |
0% to 5% (different fields) |
10-25 (carrots) |
|
July 17 |
Clinton County |
Carrots |
0% |
50 (carrots) |
|
July 11 |
S.E. Ottawa County |
Celery |
2.1% |
15-17 (celery) |
|
July 11 |
S.E. Allegan |
Celery |
0% |
35 (celery) |
|
July 17 |
N.W. Allegan |
Celery |
0% |
35 (celery) |
The differences in infectivity rate found in aster leafhoppers collected from different carrot fields in Newaygo County are similar to what we have been finding occasionally in Mason and Oceana counties this year. These may reflect differences in local leafhopper populations or differences in infection of local weed hosts.
Temperatures through the period averaged near or slightly below normal with highs of 75°F to 88°F and lows from 57°F to 70°F. The area received a trace to 0.25 inches of rain. Soil moisture remains sufficient from earlier events.
Watermelon and cantaloupe are sizing well with some early cantaloupe fields close to harvest.
Pumpkins are setting and sizing fruit.
Leaf symptoms of Phytophthora have been identified in cucumbers and the first virus symptoms have shown up in cucumbers.
Squash bug nymphs and adults and cucumber beetles can be found. Squash vine borer damage is evident.
Early tomato, bell pepper and eggplant harvest has begun.
Leaf hopper populations are high in beans.
Summer squash harvest continues. Squash bug eggs and small nymphs are becoming easier to find. Controls are needed to prevent damage. Squash vine borers continue to fly and controls could still be applied, but we’re getting past the best timing for the best control.
Foliage is very nice on tomatoes with no to very little noticeable foliar diseases. No local harvest yet.
Radish and lettuce harvest continues.
Cabbage looks good. Early planted crops are being harvested and late season cabbage is growing nicely. Cabbage moths are present.
Celery is developing nicely. Continue to monitor leafhoppers and control them where needed to prevent the spread of aster yellows.
Onions are beginning to bulb. Be on the lookout for thrips.
Early harvest sweet corn looks very nice with very little corn borer and no earworm damage seen yet.
Seeded vine crops are filling rows nicely. Some pickle harvest should begin soon in the Grand Rapids area. No symptoms of downy mildew in this area are being seen, but be on the look out for it, especially as fields are nearing harvestable size.
We have had fairly heavy rains overnight on soils that already had adequate moisture. We are still discovering new damage from last week’s storm. For instance, it will take years to replace damage to windbreaks.
In asparagus, fern pushed over by last week’s wind is already sprouting new spears. Unfortunately, the old fern really didn’t have a chance replace the energy that was used to grow it, so this wind damage could lower yields next year, especially if care is not taken to protect this new fern from insects and disease. Tom-Cast sensors have generated a lot of disease severity values over the last week, so purple spot should be a real threat.
Disease severity values have also jumped greatly in carrots. Cercospora seems to be the major disease problem this year. Most growers have already put on a second nitrogen application and some are nearing a third application.
A few virus-like symptoms are showing up in zucchini. I have a sample at Diagnostic Services, but haven’t heard any results yet. Phytophthora is showing up in severely infected fields and this rain will only make matters worse.
Corn earworm activity reported in sweet corn. I have caught two more adult moths in my trap.
Overall growing conditions continued favorable during the past week with normal temperatures and adequate precipitation. Rainfall amounts recorded at the MAWN weather stations at Ludington (Mason) and Fremont (Newaygo) were almost identical with 0.66 and 0.64 inches, most of which came on July 20. Conditions have remained favorable for disease development with higher humidity and dew points.
Carrot harvest should be underway this week. Aster leafhopper numbers have been reported to be higher this week where fields have not received pesticide applications.
Snap bean harvest began in Mason County this week.
European corn borer counts this week (July 24) at the Mason County site were 0, 0 and 8. No corn earworm were found at the Mason County sweet corn site.
Harvest of summer squash and slicing cucumbers continues. Harvest of hand pick pickling cucumbers has begun. Fungicide programs for the control of downy mildew are being applied.
A mostly west to east zonal jet stream is expected across North America for much of the upcoming week with the passage of several weak weather disturbances through the Great Lakes region. Given good low-level moisture inflow from the south, this weather pattern should lead to very summer-like temperatures and an almost daily chance of scattered showers and thunderstorms through at least the end of the workweek into the early weekend.
Rainfall chances over the next few days will be greatest across southern and central sections of the state and during the late afternoon and early evening hours when atmospheric instability is greatest. Precipitation totals through the weekend are expected to range from less than 0.25 inches in extreme northern sections of the state to 1.0 to 2.0 inches across the southern Lower Peninsula. Temperatures will remain at above normal levels for the next seven days with means running 4 to 8 degrees F above the climatological normals. Much of this departure from normal will be associated with abnormally warm nighttime temperatures. High temperatures during the next several days will generally range from near 80 in the far north to the upper 80s south with lows ranging from the low 60s north to the low 70s south. Dew point temperatures will likely approach or exceed the 70°F mark once again, with heat index values rising into the mid and upper 90s later in the week. Highs may increase into the low 90s across inland areas of the state by early next week.
In the medium range forecast, latest guidance suggests upper air ridging over the central United States with troughing over New England and over the Pacific Northwest. The forecast pattern is similar for both 6-10 and 8-14 day periods, although the central ridging feature is expected to be flatter (more west to east) in the 8-14 day time frame, which should allow for a more active weather pattern in the Great Lakes region.
Both 6-10 day and 8-14 day outlooks from the NOAA (covering July 31 through August 2 and August 2-8) call for above normal temperatures state- and region-wide. Precipitation totals during the 6-10 day time frame are forecast to range from near normal levels in extreme southwestern sections of the state to near below normal levels elsewhere. During the 8-14 day time frame some moderation in precipitation is forecast with near normal totals forecast statewide. Forecaster confidence in these outlooks is considered greater than normal due to good agreement between individual forecast tools and temporal continuity in recent forecast model runs.
Near normal sea surface temperatures in the central and eastern equatorial Pacific region are expected to continue over the next several months, which should lead to neutral ENSO conditions. Without an ENSO event, the NOAA Climate Prediction Center long lead outlooks for the United States are based primarily on long-term trends and on existing and recent soil moisture conditions. For the month of August, warmer than normal temperatures are favored over western, central, and southern sections of the United States with drier than normal weather expected across portions of the southern Great Plains and west coast regions. Wetter than normal weather is forecast for sections the northern High Plains region.
For the northeast one-quarter of the country including Michigan, the outlook calls for the climatology or “no direction” scenario for both mean temperatures and precipitation totals, with near equal odds of below-, near-, and above normal values forecast. Further ahead, the 3-month (August through October) outlook for Michigan calls for increased odds of above normal temperatures and for below normal precipitation.