Renovating Strawberries to Reduce SWD Populations

Laura McDermott, CCE ENYCHP and Juliet Carroll, NYS IPM

Strawberry renovation is a critical, but often overlooked part of growing June bearing strawberries. This year, with SWD numbers climbing, it’s even more important to remove fruit leftover in the field as quickly as possible. Otherwise, this fruit can serve as a food and reproductive resource for SWD population growth.

Renovating the short day plants that we call June bearers (they are called short day because they set their buds in the crown in the fall when days are short) is critical because it provides an opportunity to control weeds, diseases and insects when you mow the plants, and then helps provide more room in a dense row for remaining plants to send out new daughter plants which will thrive.

Renovation Process – Immediately after Harvest is Finished:

1. Ensure the field has adequate soil moisture. This is VERY important. If you have not had at least 1” of rain/irrigation per week for the 2 weeks prior to renovating I would not mow the plants. Likewise if heat stress occurs right before renovation – proceed with caution.
2. Apply 2,4-D if needed. If you don’t have a heavy weed load you don’t have to do this, and many growers have decided that 2,4-D is too unreliable. I will say that the new formulations are much more predictable in the way they behave, but still some growers have seen plants set back after this application.
3. Wait 5 days after 2,4-D is applied to mow. If 2,4-D is not used, mow immediately after picking.
4. Fertilize. This is when the majority of nutrients are applied to the plant. 70 lbs of actual N/acre is recommended at this time. You will be adding more nitrogen in September and that rate will be guided by the foliar sampling you do in early August.
5. Narrow the rows, cultivate middles of wide rows. Throw ½” of soil over remaining crowns.
6. Apply pre-emergent herbicide (ie Sinbar – make sure to read labels as some varieties are sensitive).
7. Irrigate.
8. For fields with leaf diseases (leaf spot, leaf scorch, leaf blotch, leaf blight), a fungicide application 7-10 days after renovation will help protect the new developing leaves from infection.

The task that creates a lag in the renovation process is the 2,4-D application. Most growers want to apply this herbicide all at once, so early berries are forced to wait weeks for the late varieties to finish – and in the case of ‘Malwina’, growers could delay renovation for more than a month. This tactic leaves a continuous supply of unharvested, cull fruit that SWD can develop in. A further delay is due to 2,4-D needing to be taken up by the leaves — mowing is delayed for 5 days to allow the weeds to absorb the herbicide. Given this added delay from choosing 2,4-D, growers need to make sure the weed species in their field are vulnerable to 2,4-D. If not, don’t delay renovation to use an ineffective herbicide, choose an alternate herbicide, and mow the planting as soon as picking is finished.

Whenever possible, mow the variety as soon as harvest is done. Be aware that mowing a water- or heat-stressed field can result in poor re-growth. Therefore, make sure the plants are well watered prior to mowing. If temperatures are above 90 degrees and you cannot irrigate, mowing should be delayed. If irrigation is not possible, consider skipping the mowing – but still renovate by narrowing the rows and throwing some soil up over existing crowns.

When strawberry fields go out of the rotation, remove them from production as soon as possible by tilling and then seeding a cover crop or a late season vegetable. If you cannot till the field, then mow it close to the crown or cultivate aggressively to help crush and dry down the remaining berries. This will help destroy this resource and limit SWD population growth in the remnant fruit.

For more in-depth information re: strawberry renovation, visit http://www.hort.cornell.edu/fruit/nybn/newslettpdfs/2014/nybn1306.pdf.