If your strawberry field just “squeaked by” this spring with a moderate crop of fruit but maybe a not-so-attractive weed problem, it may be an easy decision to plow it up after harvest is finished. One of the more difficult decisions, however, can be whether to keep a vigorous strawberry field another year if it met or exceeded expectations. Reasons to renovate include multiple variables. Scouting prior to making a decision on renovation is in order; make notes on pest hot spots and keep in mind how difficult that particular pest is to control with the methods you have available.  Let’s take a look at some of the factors involved in whether to renovate or rotate that field out of strawberries for a number of years:

• Weed populations– Weeds can get out of control quickly if they are perennial like quackgrass, field bindweed or Canadian thistle. Other very difficult weeds include chickweed, dandelions, white cockle (tends toward perennial) and oxalis. These may have been pre-existing problems that were ineffectively controlled prior to strawberry planting; or started post-planting due to weedy mulch or border weed populations seeding the field. Whatever the reason, these weeds compete for nutrients, water, light and serve as alternate hosts for diseases and harbor many insects. Weeds can make a strawberry field just plain unsightly for customers and severely impact profitability!
• Diseases– Especially if a grower has a heavier loam or clay soil and is growing some cultivars that have limited resistance, black root rot complex, red stele and Verticillium wilt diseases can take their toll on plant populations, resulting in breaks in the row and generally poor vigor and productivity.
• Insects & Mites– Cyclamen mites tend to build up over time unless a very strict control regimen has been established; even then, the fear of spreading them to unaffected areas of your farm is enough to make anyone want to rotate out of a field, no matter how young. Cyclamen mites can be brought in on nursery stock or from a different farm. Black vine weevils and root weevils also tend to build up over time and move across older fields and can infest young fields if not brought in to check.
• Winter Injury/Plant stand– Winter injury was severe in some parts of the state this year and strawberry fields were not exempt. Maybe the cultivar planted already did not have a good reputation for winter hardiness but had been hoped “it might make it”. Well, wasting money on non-hardy cultivars is not a good business decision and winter hardiness has a way of creeping up and eating into your profits. Reduced plant stands are typically the first aspect one sees as a result of winter injury but if not severe enough to kill the plants outright, fields might just seem unthrifty or recover slowly from pest infestations. Your barometer of choice to measure field productivity is going to be your record book. What were the yields this year versus last? How has the plant stand changed from last fall prior to mulch application compared to May/June of this year?

In general, if the plant stand is less than 70% and there is a large or serious population of a particular weed, insect, mite or disease pest, one should plow the field under and rotate out of strawberries for 3-5 years.

So, let’s turn to the situation where your field looks great; is there any question on whether to retain it and renovate? Yes! It is always a good idea to consider the long-term rotational viability of your farm. Some growers have been able to maintain a strawberry planting for 7+ years and never had to replant. Well, the long-term viability of that age of field has been reduced significantly for any future replant of strawberries. Even though it may not be immediately obvious looking at a profitable field, there are subtle diseases, nutrient problems, insects, soil microorganism changes occurring that will preclude that field from sustaining another successful strawberry planting for probably many years. Sustainability is the key word in our discussion and typically, strawberries should be only allowed to produce about 3 crops before rotating out.  This issue becomes even more serious if a grower has minimal acreage to work with for rotation or has a more limited arsenal of controls (organic growers). The less land you have available, the shorter amount of time a strawberry field should be retained, no matter how good it looks. There are many examples that I could relate where keeping a field for just 2 harvests would be appropriate. These include: 1. first year fruiting fields should have the best yield of any year of the planting. 2. younger plantings are more likely to survive a severe winter due to deeper rooting, thus preventing crown exposure. 3. As fields age, older plants with multiple crowns will typically produce progressively smaller fruit each year. On the other hand, if you have plenty of land, longer rotations may not be an issue and keeping that field for 5-6+ harvests (with good renovation) may be the most financially sound. Estimates vary but starting a new field up to first harvest will include about 125 hours of labor/A, $400.00 in supplies and probably a plant cost of around $1,500/A. Grand total estimated at $3,650/A, excluding machinery and well depreciation, fuel, repairs and maintenance.

If the decision has been made to renovate instead of rotate, let’s look at some of the major advantages of rotation. In most cases, it is much cheaper to renovate than starting a new field the next year. Even though there may be some significant pest problems, a complete renovation allows us to reduce disease inoculum levels, insect/mite populations, target invasive weed populations, narrow, thin-out and readjust plant density and invigorate older plants while encouraging the production of younger, more productive plants. Most of these beneficial effects also lead to less susceptibility to winter injury.

The steps and methods for successful renovation depend on many factors unique to your farm and location. Renovation is most effective if begun as soon after the last harvest as possible. Traditionally, the first step of renovation is the application of the broadleaf herbicide 2,4-D amine form, like Formula 40. This can be beneficial if the broadleaf weeds in your field are taller than the strawberry plants. However, typically many of the troublesome broadleaf weeds are shorter (chickweed, dandelions, oxalis) and under the strawberry canopy, thus requiring either a 3-nozzle set-up for each row with 2 of the nozzles angled to hit at the base and underneath the strawberry leaf canopy on either side of the row or wait until you do a tall mow and then spray the 2,4-D. Either way, 2-4 days should expire before going to the next step to allow weeds to absorb the herbicide. An alternative to 2,4-D is the use of Stinger herbicide (special 24C registration in WI). Apply 1/3-2/3 pt/A in 20-75 gal. of water/A. It should provide great post-emergent control of groundsel, oxalis, curly dock, thistles and dandelion (full rate). It will only suppress chickweed.

Mowing may be the first optional step depending on your location and pest problem. However, new runner plants that form after renovation are always behind the development of those in a new field, so every few days in delay make a difference in the yield capacity for next year. If you delay renovation and/or are located in northern WI, it may be advisable to not mow off the leaves as one of the steps in renovation, as this process delays runnering by more than 2 weeks. Mowing may also be inadvisable/unnecessary if there are few leaf diseases or other pests present OR if plants are stressed by drought or have root diseases that compromise the ability of these weakened plants to produce new leaves. Mowing would be advisable, especially if there is a cyclamen mite problem. This is the only way to expose the crown enough to get sufficient control from the miticide/insecticide applied. Mowing height should be about 1-2” above the crowns.

One step that is easy to forget is subsoiling. Multiple tractor passes through the field and human traffic during harvest can cause considerable soil compaction. Add the effects of moldboard plowing over the years for field preps and there is a real need to break up hardpans.  A probe can be used to determine the depth of the hardpan but most subsoiling procedures will penetrate 2’ or more. Subsoiling helps relieve excess soil moisture, reduce compaction effects, improve water percolation and better prepares the soil for tilling by mixing straw with the soil. Subsoiling too deep or when the soil is too wet to shatter can make things much worse than subsoiling at all!

The step that is almost always required is to narrow the rows to 8-12” wide with a rototiller or disk. The width you narrow to depends on the vigor of the cultivar. Cultivars like Honeoye and Cavendish should be narrowed to 8” while less aggressive plant-makers like ‘Jewel’ should be only narrowed to 12”. Taking some of the middle tines out of your rototiller seems to work the best as digging deep with a rototiller will help throw extra soil over the top of older crowns which in turn, helps them root back in the soil (1/2-3/4” of soil thrown over the old crowns would be ideal). Multivators (tool bars with individual rototiller heads) are often insufficiently aggressive for renovation operations.

A preemergent herbicide application is typically next. Some of the herbicide options include: 1. Spartan 4F can be applied in 20-40 gal. water/A for good preemergent control of groundsel, lambsquarter and pigweed. 2. Sinbar can be applied at 4-8 oz/A in 20+ gal. of water after all mowing, row narrowing and subsoiling. The strawberry cultivars Kent, Cavendish and Annapolis are known to be sensitive to higher rates and more injury is likely if Sinbar applications follow 2,4-D. Sinbar provides good preemergent control of annual grasses and many broadleaf weeds (excellent on chickweed).

Most renovations include addition of fertilizer to invigorate plantings after the stress of fruiting and to encourage new leaves and runnering. Although fertilizer applications usually involve just nitrogen, if prior tissue or soil tests indicated the need for a low soil mobility nutrient such as potassium, then the fertilizer could have been applied just prior to row narrowing to facilitate incorporation into the root zone. If only nitrogen is being applied, use about 50 lb. of actual N/A on loamy or clay soils and a split application of 30-40 lb. actual N at renovation and then another about 3 weeks later.

Consistent irrigation post-renovation is critical for plant recovery, herbicide activation and fertilizer absorption. Ideal moisture levels can be maintained by watering once loamy soils reach about 50% of field capacity (about 5-8 days between watering) and sandy soils reach 60-65% of field capacity (approximately every 2-4 days).

This article was posted in Berries and tagged strawberry renovation.