Next year’s strawberries and raspberries may be the furthest thing from your mind now, but this is a critical time for both crops. It’s in August and September that cell size of the spring fruit bud is determined. The more favorable the growing conditions now, the bigger the cells this fall, which means bigger berries in the spring. Just a week without water can stress the plants.
A University of Missouri study showed that it took only two late summer irrigations to increase strawberry yields in the spring by more than 5,000 quarts per acre. You can maintain strawberry plantings for several fruiting seasons if you properly manage and renovate them after harvest. Renovation is not recommended for day-neutrals or ever-bearers however.
After the crop has been harvested, mow the foliage to about two inches above the top of the crowns. You can use hedge clippers or a rotary lawn mower with the blade raised high. Be careful not to damage the crown of the plant. Remove the plant debris and bury it.
Narrow the rows to a strip 8- to 10-inches wide using a rototiller, or hoeing no deeper than 1- to 2 inches. Thin out old and weak plants. The best plant density is about five to six plants per square foot of row.
Keep the planting weed free by cultivating. Loose soil also promotes rooting of runner. Remove all excess runners as they form. All excess runners should be removed by Sept. 1 since they won’t have time to root and form flower buds for next season’s crop. Strawberries should be fertilized now. For plants set out this last spring, apply 4 to 6 ounces of ammonium nitrate or 12 to 18 ounces of 10-10-10 per 25 feet of row. Brush fertilizer off the leaves to avoid leaf burn. For plants in the second year of growth, increase the application rate to 6 to 8 ounces of ammonium nitrate or 18 to 24 ounces of 10-10-10 per 25 feet of row. The more favorable the growing conditions for strawberries in August and September, the larger the fruit will be next spring. Just a week without water can stress the plants resulting in smaller spring berries.
Once raspberries have finished fruiting for the year, it’s time to prune. Remove all of the canes which bore fruit this season. The pruning exposes the new canes (those that will bear fruit next year) to the light and gives them a chance to develop. Retain 10 to 12 of the healthiest new canes for the next year’s crop. For fall-bearing cultivars of raspberries, remove the top half of the cane after fruiting is over, if you want a light summer crop the following June. Because the fall crop on fall fruiting raspberries is superior to the summer crop, WSU horticulturists advise cutting all canes to the ground in mid-October. New canes will grow next spring and produce fruit in the fall.
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Right on schedule, fall webworm infestations are beginning to appear on deciduous trees and shrubs throughout our coastal area. Their large, conspicuous tents are often mistaken for those of the notorious tent-caterpillar which appears in early spring. Although these critters may look awful, they are generally not a threat to our trees and shrubs.
Fall webworms are usually found in groups and feed together on the foliage of their host plant. They are unique from the standpoint that they skeletonize and consume the leaves under the protection of a tent-like web which they enlarge from time to time as they develop and more food is needed. Large portions of a tree may be covered by these webs.
The caterpillars feed entirely within the tent, which protects them form predators and parasites. The tents also help with mechanical control. When the “tented” branches are within reach, they can often simply be snipped off and destroyed.
While the webs and accompanying defoliation caused by fall webworms are unsightly, trees do not die as a result of being defoliated by caterpillar pests. For most gardeners, it is the unsightliness of the webbing and defoliation that causes the greatest concern.
Out of reach webs can easily be removed by using a hook fashioned from a coat hanger taped to the end of a long pole or a large nail driven through a long pole (exercise appropriate caution around power lines). Destroying the web in this fashion also exposes the caterpillars to predation and parasitism. Yellow jackets, paper wasps, birds, predatory stink bugs and parasitic flies all feed on webworms. Burning webs is not a good idea. Twigs and branches that are defoliated by caterpillars will produce new leaves; twigs and branches killed by fire will not.
Chemical control should be used if the infestation is heavy, or if tents are high in the trees and difficult to reach. Bacterial insecticides containing Bacillus thuringiensis are formulated specifically to kill feeding caterpillars without harming other insects. Thoroughly cover the leaves next to the nests. As these leaves are incorporated into the nest and eaten, the Bt will be ingested.
Donald D. Tapio is a regional gardening and farming specialist for Southwest Washington, having retired from Washington State University’s Extension Office. This column expresses his personal opinions and tips after decades of research. Contact him with non-gardening questions by emailing the editor at firstname.lastname@example.org. Those with gardening questions should contact a WSU Master Gardener volunteer at email@example.com.