Heat & humidity are great for our gardens but can also trigger the appearance of numerous pests and diseases.  Along with the great growth we’re seeing and early harvests of greens, peas, & summer squashes it’s time to keep a keen eye to detect and control any problems before they become serious issues.  Healthy, well-watered plants can tolerate most pests and diseases, but plants may need our help when conditions in mid-summer are ideal for unwelcome insects or plant disease organisms.  Let’s look at what’s happening now in the garden and some near future issues that we can prevent.

First, some Good News.  Monarch butterflies have returned to Vermont from their Mexico wintering grounds.  Along with their look alike Viceroys that do not migrate and have a black stripe across their rear wings (Monarchs do not) and the yellow Swallowtails we can now enjoy these beautiful, beneficial (pollinator) insects foraging flower beds and open fields.  If you have a butterfly friendly yard with Zinnias, Joe Pye Weed, Butterfly Weed, Bee Balm, Cone Flowers, Milkweed, etc. these plant species are to be protected and enjoyed.  Swallowtail caterpillars are already large and feeding on dill plants.  The butterflies are worth sharing a few dill plants so they keep coming back.

Are you a Deadheader?  As gardens fill with blossoms it’s time to keep removing the older flowers (“deadheading”) to encourage a re-supply of new blossoms.  This works very well for most annuals like marigolds, petunias, zinnias, snapdragons, geraniums, salvia, nasturtiums, and even some perennials like the day lilies now in full bloom.  Remember, the purpose of flowers is for the plant to reproduce by making seeds.  Once the plant has mature, pollinated blossoms with seeds inside it gets the signal that its job is done and no more flowers are needed.  Removing those maturing blossoms prevents that “time to retire” message and the plant will keep giving us more flowers. 

Elderberries are in full bloom right now and can be seen along roadsides in lower, moist areas.  If you want to enjoy elderberry pies, wine, jelly, etc. this fall but don’t have any growing in your yard, now is the time to go “hunting” elderberries and mark their locations.  They are easily seen by their multiple white blossom crowns on bushes.  They will be nearly impossible to find in late summer when their unique, nutritious berries are ripe so find them now.

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Plants need water!  You know that, but do you know that how you water makes a big difference.  This has mostly been a dry summer and water has become a limiting factor for many gardens and lawns.  The rules to watering correctly are simple:  Water deep and water roots, not leaves.  Sprinklers or spraying plants seems good but actually can cause disease problems without providing enough water.  Except for lawns, watering should be done to avoid getting the foliage wet by watering the soil directly with a hose, soaker hoses, or drip system.  It is far better to water very deep, infrequently, directly under your plants and then let the surface soil dry out in between watering to reduce weed and disease growth.  The best time of day to water is in the morning so that plants have time to take up the water in preparation for a sunny day of photosynthesis.  This also avoids moist leaves into the night which encourages the growth of disease fungi.

Humidity Alert!  Yes, it’s not the heat, it’s the humidity that encourages the growth of many plant diseases.  Mid-July has brought ideal conditions for fungi but here are a few tips for reducing disease damage in your gardens.

Tomatoes.  Keep them upright with supports.  Prune away side shoots (suckers) to open them up for ventilation and sunshine penetration.  Apply weekly preventative sprays now through August to inhibit diseases from getting started.  Once infected, it isn’t possible to cure the disease, only to remove it.  Organically approved preventors include Serenade (a natural beneficial bacteria that competes with infectious fungi), copper fungicide (blocks the growth of fungal spores), sulfur powder (creates an acid that inhibits fungal growth), and compost tea.  I prefer to rotate between different spray applications using a different one each week.  I also include foliar fish fertilizer as a supplemental food to keep plants extra healthy.  Compost tea has become a popular practice based on numerous university studies that have confirmed its effectiveness.  Here’s a short DIY video to help you get started.

Squash & Cucumbers.  As Cucurbits start producing their fruits they become susceptible to Downy Mildew, a fungal infection that is encouraged by the current humid weather.  Prevention and delay are key.  They need a steady supply of nutrients and water to yield full fruits and stay healthy, so it’s important they have been well fed with a side dressing of compost or organic granular fertilizer and are well watered during the dry spells.  A weekly spray on the leaves of fish fertilizer plus compost tea is a good feed and disease preventer.

Apples.  Web worms and other caterpillars have emerged and are attacking the foliage of apples now.  Look for dead brown leaves near the ends of tree branches or rolled/folded leaves.  Web worm caterpillars strip off the underside epidermis (skin) of the leaves to eat the leaf tissue turning the leaf brown.  Caterpillars build a sticky web around themselves or fold the leaf with a web for protection from birds so spraying with the usual Bt (Dipel) organic bacteria for caterpillars has limited effect.  Physical removal by pruning off the affected branch will eliminate them.  If you don’t want to cut off the branch, then burning the infested leaves along with the caterpillars (but not the branch itself) with a small butane hand torch is effective.  For individually folded leaves just open them and squash the little caterpillar inside.

Raspberries.  Just as berries start to ripen sawflies larvae are emerging.  Look for curled, web bundled leaves covered with ¼ inch larvae on the undersides.  Snip them off and dispatch by fire.   We also have a minor problem with cane borers in raspberries.  If you see a severely wilted tip of a cane and find a pair of rings around the stem down about 3 or 4 inches that is cane borer.  The larva is inside the cane between those two rings blocking the flow of sap to the tip.  Just break off the effected cane at the rings and discard far away from your raspberries.  Coming soon… Japanese Beetles.

Insect scouting is essential to successful gardening – keep a sharp eye out for signs of damage or suspicious changes in plants (usually the leaves) every time you are in the garden.  Daily inspections can catch a problem before it gets serious.

Tick Check.  There are ticks in the area and we need to be very watchful for them on ourselves and pets.  Ticks carry some serious diseases and are one of the hazards we now need to deal with.  Use repellents, tuck your pants into socks, and inspect.

Remember to compost your food and yard wastes for the best garden fertilizer.  Here’s another short video to help you get your own compost started.

What are you seeing on in your garden?  Got questions?  Bring your plant or bug samples to the Mount Holly farmers’ market Plant Clinic on Saturday mornings.