Beware of thrips on strawberries

Although strawberries are not considered to be a vegetable crop, using VegNet is a good way to get information out to growers who have both vegetables and berry crops.

Strawberry fruit that have been injured by thrips are a dull or bronzed color, and are often small, hard, seedy, and fail to ripen. They can cause uneven maturity of fruit. When severe, their injury can make the strawberry crop completely unmarketable.

Thrips are an occasional serious pest of strawberries. This means that in most years, they are not a problem, but in some years, they can be a big problem. One such year was 2018 for some growers in Ohio. As far as we understand the problem, the reason for variability from year to year has to do with weather systems. In some years, conditions are right that large numbers of small insects such as thrips and leafhoppers are carried on strong weather fronts moving from the southern USA into Ohio during the time that strawberries are in bloom. In other years, this long-distance movement does not happen at all, or happens later, at a time when strawberries are no longer in bloom.

Thrips are small, slender, elongate, cigar-shaped insects, about 1 mm (1/25 inch) long. They differ from other insects by having narrow strap-like wings that are fringed with hairs (Figure 1). The wings are usually folded lengthwise over the back when they are resting or feeding (Figure 2). They have asymmetrical mouthparts (Figure 3) that have a well-developed left mandible and an underdeveloped right mandible. They feed by piercing plant cells by the mandible then sucking sap that oozes out of the punctured cells. Thrips generally have flowers as their preferred plant part. They are found in flowers of many species of plants. Thrips are often overlooked due to their small size and their tendency to hide in protected places. When present at low density, thrips are often not harmful to plants.

The thrips species that infests outdoor strawberries is Frankliniella tritici, which has the official common name of ‘flower thrips’, but which is widely known as the eastern flower thrips. It does not tolerate cold weather well so does not survive winter well in places like Ohio. The adults are yellowish brown, and the larvae are whitish-yellow. The larvae are similar to the adults in shape but smaller and without wings. On strawberries, the infestation starts by adult thrips during bloom but then can continue during fruit set by adults and their offspring larvae. Thrips hide under the cap of the berry or in grooves around the seeds on the berry.

A key to thrips management is frequent monitoring, at least once per week. Growers should examine early flower clusters on early cultivars. In each of five to 10 areas of the field, five to 10 blossoms should be tapped into a white cup, or into a zip-top sandwich bag, which should then be examined for the dislodged thrips running around on the surface. Count the number of thrips found, then calculate the average number of thrips per blossom. A rough action threshold for treatment with insecticide is the presence of 2 or more thrips per blossom. Once fruit are ¼ inch in diameter, an action threshold is 0.5 thrips per fruit. If thrips are above threshold, the trickiest part of management is to avoid spraying insecticide that will harm pollinators. Insecticide should be applied pre-bloom or before 10% of the plants have open blossoms. If thrips are found above threshold on early cultivars, then a preventive spray can be made on the later cultivars before their flowers open, to avoid harming pollinators.

Insecticides used to control thrips on conventional strawberries are Radiant, Assail, and Sivanto, all of which have thrips listed as a target pest on their labels. Thrips are well controlled by Lorsban, Brigade, and Danitol, which are allowed for use on strawberries, but thrips are not listed as a target pest of the label of these three products. Note that Lorsban has a 21-day pre-harvest interval. Products for thrips control on organic strawberries are Entrust and azadirachtin products such as Neemix and Aza-Direct.

If a biological control approach is preferred, several kinds of natural enemies are available for purchase from commercial insectaries for thrips control: Orius (predatory flower bugs), and two species of predatory mites: Amblyseius cucumeris and Ambylseius swirskii. Biocontrol is not feasible to begin once the thrips population is large but can be planned in advance at locations that have a consistent problem with thrips.

Figure 1. Typical appearance of a thrips.

Figure 2. A thrips with wings folded over its back.

Figure 3. Close-up of thrips head and mouthparts.

by Celeste Welty, Extension Entomologist

Magister, a new miticide, has expanded registration

Magister SC Miticide from Gowan Company is now registered for use on many specialty crops. Although it is called a miticide because it controls spider mites and rust mites, it also controls some insects (psyllids and whiteflies), and powdery mildew on some crops. The active ingredient is fenazaquin. Its mode-of-action group as a miticide is 21A, the same group that contains Nexter, Portal, Torac, and Apta. Magister kills mite eggs by contact, and kills mite adults and immatures by contact and ingestion. For fungicidal activity, it is in FRAC group 39. Magister is highly toxic to bees, so care must be taken to not spray it on blooming crops or weeds.

Magister has been registered for a few years for use only on hops and cherries. Vegetable crops now on the label are cucurbits (3-day PHI), fruiting vegetables (3-day PHI), and legumes (7-day PHI). Small fruit crops now on the label are blueberries (7-day PHI), caneberries (7-day PHI), strawberries (1-day PHI), and grapes (7-day PHI). Tree fruit crops now on the label are pome fruit (7-day PHI) and stone fruit (3-day PHI). Hops are also on the label (7-day PHI). The label specifies a limit of one application per year on each crop, and a 12-hour re-entry interval. The rates are 24-36 or 32-36 fl oz per acre, depending on crop.

-Celeste Welty, Extension Entomologist

SPRING ROLLER COASTER RIDE COMING – Jim Noel

It is spring and with it often comes wild swings. This is what we expect for the rest of April 2019.

 A parade of storms will begin later this Thursday into Friday and follow every 3-5 days. This will cause 2-3 inches of rain on average for Ohio the next two weeks as shown in the attached graphic. Normal rainfall is now almost 1 inch per week. Hence, slightly above normal rainfall is expected. The one exception could be northern and northwest Ohio where it is possible to see less rainfall depending on the exact storm tracks.

We are also fast approaching our end of the freeze season typically in mid April up to around the 20th for much of the state. Some places in the north it can be late April. Right now, everything looks like a normal end to the freeze season. We do see the possibility of another freeze this weekend on Sunday AM especially north of I-70. A few more could happen into the next week or two before coming to an end.

Temperatures are expected to overall be slightly above normal for the rest the rest of April but with wild swings. This should help bring 2-4 inch soil temperatures into the normal range, possibly a degree or so above normal. The exception would be northern Ohio where above normal ice levels this past winter on the Great Lakes will keep water temperatures on the Lakes lagging and may keep air temperatures closer to normal there.

With all the storms lined up, we do expect a windy April as well. Winds of 30-40 mph with gust to 50 mph can not be ruled out Thursday or Friday this week with storm number one. 30-40 mph winds will also be possible with the storm later Sunday into next Monday and can not be ruled out with the third storm later next week.

After a wetter April indications are for a warmer and not as wet May with the possibility of normal or even a bit below normal rainfall.

Early indications for the summer growing season are normal or slightly above normal temperatures and possibly a bit wetter than normal though June could be a bit drier.

https://www.weather.gov/ohrfc/SeasonalBriefing

Other early indications give the possibility of another wet harvest season.

National Weather Service
Office:
1901 South State Route 134, Wilmington, OH 45177
Phone:
937-383-0430
Specialization:
Weather, Flooding, Climate impacts
Biography:

Jim Noel is currently the Service Coordination Hydrologist at the NOAA/National Weather Service’s Ohio River Forecast Center (OHRFC). He started in the National Weather Service in 1992 and has been with the OHRFC since 1996 as a hydrologist.

2019 Spring Planting Update for Central Ohio

Our first sunny days in the 50’s and 60’s are here and many backyard growers, community gardeners and urban farmers are looking to get outside to start spring planting.  One important step in this process is to make sure the seed that you are using will have decent germination rates to ensure that you do not start with a crop failure at the beginning. Click HERE for a link to vegetable seed viability times.

Have you soil tested your vegetable garden recently? Making sure that you have enough nutrition present to grow your vegetables is another important step in making sure that you have a productive season.  Contact your local Extension office to find out about soil testing kits for purchase.

The National Weather Service Climate Prediction center has their three month projection for April-May-June for temperature and precipitation.  (LINK)

The three month precipitation prediction calls for a greater than normal chance for increased precipitation.

 

The three month temperature projection calls for a greater chance of warmer than normal conditions.

One very important variable to monitor is soil temperatures.  Since seeds are in primary contact with soil and need that seed-soil contact to germinate, it is more important to monitor soil temperature than air temperature.  Certain seed varieties will need certain temperatures based on what family of vegetable they are in.  Most spring vegetables germinate reliably in cooler soil than summer vegetables.

Currently soil temperatures as monitored by the Columbus Station (Waterman Farm) of the OARDC Weather System are around 40 degrees F at 5 cm and 10 cm soil depth.  (LINK) If you garden in a raised bed, you may have warmer soil than a level garden plot.  This may allow earlier planting than normal.

Make sure that you do not work the soil via tillage if it is too wet, especially with the heavy clay soils common in central Ohio.  This could create a poor growing condition for the entire season if large clumps of compacted soil are created when tilling wet soil.

This community garden was mowed last fall with the residue left on top of the soil. A seed bed was created via tillage a few days ago when the soil was at the right moisture level.

If you have started transplants under grow lights in a seed station, it may be time to transplant them into individual cells.  Check out this video  that will show how to divide and transplant seedlings into cell packs. 

Good choices for spring vegetables to direct seed into the garden once your soil is above 40 degrees F:

  • Spinach
  • Radish
  • Carrots
  • Lettuce
  • Peas
  • Swiss Chard
  • Cabbage family

Seed potatoes can be planted later this week if the soil is not too wet to work.  If you wish to plant onions but are unsure if you should use seeds vs. sets vs. transplants then click on this article that goes over the benefits of each type of onion planting.

It will be time to plant transplants in the garden as soon as we get a few more degrees of soil temperature increase.  If you have transplants under the grow lights, it is important that you harden them off for a period to acclimate them to their future outdoor home.  It takes about 3-7 days of gradually introducing transplants to outdoor weather and temperature before they will be adjusted and have success in the ground. Do not forget this step, it is important to do this to minimize transplant shock.