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Wisconsin Yard and Garden Tips

June, 2016

Plant Hardiness Zones Map | Last Spring Frost Map | First Fall Frost Map
UW Extension County Offices
By Sharon Morrisey, Consumer Horticulture Agent, Milwaukee County UW-Extension
Wisconsin Yard and Garden Tips is updated monthly by Milwaukee County UW-Extension. Applicability in northern Wisconsin counties may be delayed one to two weeks in spring, and advanced a like period in fall.

June is the beginning of summer whether or not you are a gardener. I’m always a little sad to say good-bye to spring. Without summer, however, we couldn’t be dazzled by the parade of annual and perennial flowers that add so much beauty to our lives.

With the summer also come the plant pests. One of our most reviled insects is the Japanese beetle. We will know by mid to late June how serious a threat they will be since the population fluctuates from year to year. They cannot be eliminated so the strategy is to protect your most important plants. If numbers are few, knocking them into soapy water helps. If they are prolific, you might need to resort to insecticides to apply to just your roses or grapes. Milky spore is a product that is only helpful if your lawn has enough Japanese beetle grubs in the soil to be causing visible damage. Treating the lawn will never control the ones eating your plant leaves.

Get advice, information and diagnosis of yard and garden problems from the UW-Extension. Milwaukee County residents may leave a voice message or e-mail anytime. Visiting the Master Gardeners at Boerner Botanical Gardens weekdays between 10:00 and 2:00 is another option. They will also be at various local farmers’ markets throughout the summer. For more information, call the Milwaukee County UW-Extension at 414-256-4664. To send an e-mail to most any county in Wisconsin, click on Ask An Expert on the Wisconsin Horticulture website at http://hort.uwex.edu .

First Week

June 1st is considered to be safe to transplant tomatoes to the garden. Plants with spindly stems can be buried in a trench up to their first set of true leaves.

Don't fertilize tomatoes until the first fruit has set. Too much nitrogen will cause leafy growth at the expense of flowers and fruit. Most other plants, however, benefit from a starter fertilizer when transplanted.

June 1st is also when your first lawn fertilizer application should be made. If you fertilized earlier this spring, wait until July 4th or Labor Day to do it again.

It is too late for broadleaf weed control products or combination weed 'n feeds. Summer's heat will cause the weed killer to vaporize and drift, damaging other flowers & vegetables. Total vegetation killers such as glyphosate can be used all season but will kill everything so don’t use them in your lawn or allow overspray onto desirable plants.

Fertilize bulbs and most perennial flowers now. Bulbs are forming next year’s flowers inside and perennials are actively growing and producing flowers for you to enjoy.

Prune, transplant and up-pot houseplants since they will be growing most vigorously now due to the longer days, higher light, and warmer temperatures. Move up to a pot only one or two inches larger at a time. Fertilize them monthly.

Examine honeylocust and ash foliage for plant bugs. Control with insecticidal soap sprays if damage is heavy.

Preventative treatment for apple scab and rust diseases should have been started before bloom started. For crabapples, collecting and destroying fallen leaves all season combined with proper watering and a fall fertilizer application may be all that is really necessary since these diseases are not life threatening.

Apple trees need thinning if there is more than one fruit per 6” of stem. Put plastic, zipper bags over the young, forming fruit to prevent insect damage throughout the season. Staple the bags on either side of the stem and cut out the corners of the bags so moisture can escape. Leave them in place until the apples are full sized. Then remove them to allow them to color properly.

There are many insect pests to watch for in the vegetable garden now. UW-Extension publication A2088 “Managing Insects in the Home Vegetable Garden” provides greater detail. The following are pests that may be found in Wisconsin in June:

The flea beetle chews many small holes in the leaves of a wide range of vegetable crops especially young transplants of the cole crops (broccoli, cauliflower, cabbage, and Brussels sprouts). Cover with floating row cover to exclude these tiny, hopping bugs before they begin feeding. This covering can be left in place day and night since it is permeable to light and moisture. It also "breathes" so that heat does not build-up underneath. Be sure to seal the lower edges with soil or stones. Allow ample room underneath for plant growth.

Covering cole crop plants with floating row cover will also exclude egg laying by the cabbage moths.

Potato leafhoppers are wedge-shaped, bright green insects that cause "hopperburn" on plant leaves beginning in early June. Spray once with carbaryl or malathion and cover the entire crop with row cover to prevent invasion.

Colorado potato beetle adults, eggs and larvae can be hand picked to remove or sprayed with M-Trak, a biological control product, or with the organic insecticide, spinosid. Adults are yellow and black striped beetles. The eggs are yellow and laid in groups on the undersides of leaves. The larvae are humpbacked and red. Look for them on the stem tips. They are present almost all season.

Striped and spotted cucumber beetles transmit a bacterial wilt to squashes and melons. Adults and eggs can be hand picked throughout the season or begin preventative sprays or dusts with spinosid, neem or carbaryl as soon as seedlings emerge. Leaves of infected plants wilt only during the day but the leaf stems remain erect. Eventually, the entire plant wilts and dies.

Watch for Mexican bean beetle. To be on the safe side you can cover the entire crop with floating row cover as soon as seedlings emerge. Spray with carbaryl or spinosid or neem at the first sign of beetles or their distinctive feeding damage.

Second Week

Aphids of all types show up on a range of host plants as soon as the warm weather arrives. Look for them in newly unfurling foliage, which may be curled downward around aphid colonies. Sticky leaves are also a sign of their presence since they secrete "honeydew". Black sooty mold may also grow in this sticky substance but it does little damage since it does not penetrate the leaves. Aphids, however, do damage the plant. Spray leaves with a strong jet of water to dislodge some of them. Insecticidal soap is a low-toxicity product that provides pretty good control as long as the insects are wetted thoroughly. A second and third treatment to kill newly hatched eggs may be needed in 5 - 7 days.

Check spruce and arborvitae growing in hot, dry sites for spider mites. Tap a branch several times on a piece of white paper and then hold it very still for about 30 seconds. Mites will appear as tiny, moving black specks. If present, thoroughly wet plants with a blast of water from the hose. Repeat until no mites are found.

Continue mowing around ripening foliage of spring flowering bulb plants growing in the lawn. For best flower bud development and vigorous growth next year, allow leaves to yellow completely before removing.

Third Week

Squash vine borer adults are 1 inch long, orange and green day-flying moths that are emerging from the soil now. They lay brown, button-shaped, 1/16 inch eggs at the base of the vines of summer and winter squashes. Examine stems daily and remove eggs by hand to prevent burrowing of larvae as they hatch. Wrap lower 6 – 12 inches of stem with aluminum foil or floating row cover to prevent egg laying. Otherwise, the bases of the stems can be sprayed with carbaryl weekly for three weeks. The liquid formulations seems to be more effective than the dust.

Red sphere traps coated with Tanglefoot can be hung in apple trees now to control apple maggots. Use 1 trap per 100 apples expected.

Renovate June-bearing strawberry plantings immediately after harvest. Control any weeds that have invaded. Then, either cut back all the foliage by hand or mow over the top with the mower set high enough not to damage the crowns. Eliminate new plants growing between the rows by cultivating. Then sidedress with a 10-10-10 fertilizer. Lightly work it into the soil and water in.

Once the soil has warmed, put a 2 – 4 inch layer of organic mulch on flowerbeds and around trees and shrubs. Good mulches include shredded bark, woodchips and chipped yard waste often available from your municipality. Mulch discourages weed growth, holds in soil moisture and maintains even soil temperatures. Around trees, it may simply serve to help prevent “mower blight” to trunks. Better yet expand the mulch ring to include the entire root zone or at least out to the “drip line”. Spruces and birches really benefit from this to reduce drought stress and resulting disease and insect problems.

Fourth Week

Newly established plantings of raspberries can be fertilized now with 2 -3 pounds of ammonium nitrate.

Fertilize roses after the first flush of blooms. Use one tablespoon of a complete, low nitrogen fertilizer per plant.

Oaks, elms, and maples with one of the wilt diseases will begin to show typical wilting symptoms as the summer heats up. Watch particularly the upper crown for branches with wilted leaves. Call your county UW-Extension to assist with diagnosis at the first signs of trouble.

Pinch back garden chrysanthemums one last time. Flower buds will form on new growth and be ready for fall display.


For more information, contact Home Horticulture Agent Sharon Morrisey.

Plant Hardiness Zones Map | Last Spring Frost Map | First Fall Frost Map | UW Extension County Offices

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