It’s been a challenging spring in this guy’s garden! Despite getting the normal early start required for successful gardening in Florida, I’ve been affected by Bacterial Leaf Spot stunting my tomatoes, cutworms that reduced my watermelon plantings by half, and an eternal test of my patience in the form of a dog that seems to think my raised beds are merely a shortcut to a destination further out in the yard. My latest adversary is the most potentially destructive yet, an outbreak of Southern Armyworm (Spodoptera eridania).
Early Southern Armyworm damage on Okra seedlings. Photo courtesy of the author.
Unlike some serious garden pests that wait until the heat of summer to emerge, Southern Armyworms begin appearing in spring gardens around the end of April. Adult moths can survive mildly cold weather and venture into the Panhandle as soon as warmer spring weather arrives. Once the adult moths arrive, egg masses are then laid on the undersides of leaves and hatch in a little under a week. Once loosed upon the world, Southern Armyworm larvae (caterpillars) become indiscriminate, voracious feeders and congregate in extremely large numbers, allowing them to destroy small, developing garden vegetable plants in a manner of days. Young larvae feed on the undersides of leaves and leave little but a skeleton. As larvae grow larger, they become solitary and begin to bore into fruit. Once they’ve eaten the good stuff (leaves and fruit), large larvae turn to branches and even plant stems!
Southern Armyworm larvae feeding on Okra leaves. Photo courtesy of the author.
The good news for gardeners is that Southern Armyworm, and most other caterpillar pests, are easily controlled if outbreaks are caught early. Scouting is critical for early detection and good control. Armyworm damage generally appears from above as brownish-gray sections of affected leaves with a yellowish ring surrounding these sections, this ring indicates the current feeding zone. Affected areas will appear transparent and “lacy” due to the skeletonizing effects of larval feeding. If you see leaves that look “off” in the manner just described, check underneath for the presence of a horde of tiny greenish worms.
If found in this early stage, an application of Bacillus thuringiensis (Bt), a biological pesticide utilizing a bacterium destructive to caterpillars, is extremely effective. Bt has to be ingested by caterpillars with leaf tissue to work; thorough coverage of leaf surfaces is critical for maximum control. I generally follow up with a sequential application of Bt a day later to ensure that I achieved good coverage of the plant surfaces and, therefore, good control. Unfortunately, Bt is much less effective on older larvae. Infestations not caught early require harsher chemistries like carbamates, pyrethroids and organophosphates for adequate control.
Don’t let armyworms or other caterpillar pests destroy your garden, get out there daily and scout! You have a short window for easy caterpillar control with a harmless to people, natural product, Bt. Don’t waste it!
For more information about Southern Armyworm, other caterpillar pests, Bt, or any other horticultural topic, please consult your local UF/IFAS Extension Agent. Happy Gardening!
Adult squash vine borer moths are easy to identify, as they are reddish orange and have black dots along their upper abdomen. Photo by Theresa Friday.
It’s been a few weeks, and your squash seedlings are really starting to take off. The days are blushing with summer warmth and the flicker of lightning bugs in the evening indicates the cool nip of spring is winding down. In your garden, this has culminated in lengthening cucurbit stems that now show off a beautiful bright shade of green. Squash blossoms appear overnight and begin to expand and take shape, nestling themselves under the backdrop of slightly darker green squash leaves.
Black beauty zucchini blossom in the morning sun. Photo by Molly Jameson.
A few more nights go by, giving you a chance to explore some recipes. Maybe it’s time to fire up the grill and make grilled summer squash, sprinkled with fresh mint or thyme. Perhaps you’ll make a summer squash pesto pizza. Afterall, your basil is ready for its first harvest. If you are ahead of the game, you might even have some vine-ripening tomatoes that would pair nicely with squash in a creamy pasta sauce.
Your culinary dreams are running wild when you start to notice the wilt. You panic, and think you’ve forgotten to water the garden. But no, you’ve given your garden a consistent dose of water every morning. Your basil looks fine. Your tomatoes look great. What is going on?
Squash vine borer adult in flight. Photo by Molly Jameson.
You have fallen prey to the dreaded squash vine borer (Melittia cucurbitae).
These garden pests rely strictly on plant species within the genus Cucurbita. If the squash vine borer didn’t wreak such havoc in your summer garden, you might find its striking red and black features fascinating. Unfortunately, if your squash plants are wilting unexpectedly, this daytime roaming moth may have already done its damage.
Adults lay single reddish-brown, millimeter-long eggs on the lower end of the main stem – or on leaves, leaf stalks, fruit buds, or in the soil near the squash plant. Within one to two weeks, larvae hatch, bore into the stem of healthy cucurbits, and begin to chew their way up. Multiple larvae can infect a single plant. This blocks the transport of water and nutrients, leading to the dreadful wilt that often signifies that it is too late.
A squash plant severely damaged by squash vine borer larvae. Photo by Molly Jameson.
So, what can be done? Once the wilting has begun, you may be able to reap a small harvest, depending on the timing of infestation. Adult females emerge from cocoons from May to October in Florida and have two generations per season. They prefer cucurbit varieties with large tubular stems, such as yellow squash, zucchini, and pumpkins, but can also infest watermelon and cucumbers.
If you have some cucurbits that do not show signs of infestation but others that are on the decline, it might be worth removing and destroying the infested plants. At the end of the season, cultivate your soil one to two inches deep, as this is where they overwinter in cocoons. Destroying infested plants and cultivation can help reduce the overwintering population.
Squash vine borer larvae inside a squash stem. Photo by Molly Jameson.
In North Florida, try seeding squash indoors in March and plant seedlings in the garden in early April. The earlier you plant, the better chance you have of beating the borers. Of course, you must balance the risk of borers with the risk of a late frost.
You may also want to install lightweight floating row covers that can prevent the female from depositing her eggs. But again, it’s a delicate balance, as you do not want to prevent beneficial insects from pollinating your squash once it is producing blossoms.
Scout your plants diligently each day and keep on the lookout for eggs and adults. Adults are attracted to the color yellow, so yellow sticky traps or yellow bowls of water may lure them in. Build up the soil around developing plants to act as a shield against egg laying and boring.
A healthy straightneck squash plant beginning to set fruit. Photo by Molly Jameson.
Once your plants slow their fruit production and you’ve had your fill of grilled squash, squash pizza, and creamy squash pasta, go ahead and remove the plants to prevent late infestations that can then overwinter. Lastly, rotate areas in which you plant cucurbits each year to break borer life cycles.
Vegetable gardening involves innovation and ingenuity. A clever gardener is always striving to balance weather, timing, insects, plants, soil, and everything in between. With a little planning and persistence, I know you can prevail against the tenacious squash vine borer.
For more information about squash vine borers, check out the UF/IFAS EDIS publication, Squash Vine Borer Melittia cucurbitae (https://edis.ifas.ufl.edu/in1068).
Members of the Phyllophaga genus are found throughout Florida and most of North America. One of them is the May/June beetle. Adults are most active during the rainy season. So in parts of the country where the wetter months are May or June, the common name of this insect makes common sense. But, when an area experiences extra rain earlier in the spring, the May/June beetle may emerge from the ground in March or April. That is what has happened in the western Panhandle this spring. May/June beetles have been leaving the soil and flying to the lights of people’s homes.
The life cycle of these beetles varies from one to four years. Eggs are laid in soil each spring by females. In 3 to 4 weeks, small grubs (larvae) hatch from eggs and develop through three stages (instars), with the first two stages lasting about 3 weeks. The larvae will move closer to the surface and back deeper in the soil as the soil temperature changes. While close to the surface, larvae feed on grass roots about one inch below the soil surface. Damaged grass turns brown and increases in size over time. Heavy infested turf feels spongy and moves when walked upon. The last larval stage remains in the soil from the fall through spring. The cool soil temperatures drive the larvae deeper in the soil where they remain relatively inactive. Typically, on the third year, white grubs pupate 3 to 6 inches deep in the soil and emerge as adults.
Larvae, called grubs, vary in length from ¾ to 1 ¾ inches depending on the stages. Grubs are white with a C-shaped body with a brown head and three pairs of legs near the head. Adults have ½ to 1 inch long, shiny bodies that are dark yellow to brownish-red in color. Adults do feed on the foliage of several species of ornamental plants, but the damage is typically only aesthetic; not causing long-term harm.
Monitoring of and managing emerging adults can help with deciding on the need for insecticide control for the grubs. To catch and remove adult beetles, place white buckets containing soapy water near plants that have chew marks or areas with lights at night. Leave it overnight. The beetles can easily be disposed of the next day. If there are more than 12 in the bucket be prepared to monitor the lawn for grubs. Extra rain or frequent irrigation during the adult flight time may attract more egg-laying females.
To inspect for grubs, turn over sod to a depth of at least two-inches. If there are an average of three or more per square foot, an insecticide treatment may be needed. To confirm that they are May/June beetles inspect the darkened rear of the grub. Locate the anal slit. It should be Y-shaped with two rows of parallel bristles that point toward each other. This is referred to as the raster pattern. All grub species can be identified using their unique “butt” features.
The most effective time to control this pest is summer or early fall when the larvae are small. Remove as much thatch as possible before applying an insecticide. Spot treat the off-colored area plus the surrounding 10 feet with products containing imidacloprid or halofenozide in early summer. Follow up in the fall with insecticides such as trichlorfon, bifenthrin or carbaryl if grubs persist.
One of the things to do while stuck at home due to COVID-19 restrictions, is to look for caterpillars and butterflies in your landscape. I’ve noticed giant swallowtail butterflies (Papilio cresphontes) a little early this year. The giant swallowtail is one of the largest and most beautiful butterflies in our area. Its larval stage is known as the orangedog caterpillar. This unusual name comes from the fact that it feeds on young foliage of citrus trees.
Orangedog caterpillar. Photo credit: Donald Hall, University of Florida
The orangedog caterpillar is mostly brown with some white blotches, resembling bird droppings more than a caterpillar. When disturbed, it may try to scare you off by extruding two orange horns that produce a pungent odor hard to wash off.
I’ve had some minor feeding on citrus trees in my landscape from orangedog caterpillars. But I tolerate them. I’m not growing the citrus to sell. Sure the caterpillars eat a few leaves but my citrus trees have thousands of leaves. New leaves eventually replace the eaten ones. I leave the caterpillars alone. They eat a few leaves, develop into chrysalises and then emerge as beautiful giant swallowtail butterflies. The whole experience is a great life lesson for my two teenagers. And, we get to enjoy beautiful giant swallowtail butterflies flying around in our landscape and still get plenty of fruit from the citrus trees. It is a win, win, win.
In some cases, the caterpillars can cause widespread defoliation of citrus. A few orangedog caterpillars can defoliate small, potted citrus trees. Where you cannot tolerate their feeding habits, remove them from the plant. But consider relocating the caterpillars to another area. In addition to citrus, the orangedog caterpillars will use the herb fennel (Foeniculum vulgare) and rue (Ruta graveolens) as a food source. Some butterfly gardens plant citrus trees to provide food for orangedog caterpillars so that they will have giant swallowtail butterflies. So you could plan ahead and grow some fennel, rue or find a butterfly garden in your area for the purpose of relocating the larvae.
Yellow giant swallowtail butterfly on pink garden phlox flowers. Photo credit: Larry Williams
The adult butterflies feed on nectar from many flowers, including azalea, bougainvillea, Japanese honeysuckle, goldenrod, dame’s rocket, bouncing Bet and swamp milkweed. Some plants in this list might be invasive.
Keep in mind that mature citrus trees can easily withstand the loss of a few leaves. If you find and allow a few orangedog caterpillars to feed on a few leaves of a mature citrus tree in your landscape, you and your neighbors might get to enjoy the spectacular giant swallowtail butterfly.
More information on the giant swallowtail butterfly is available online at http://edis.ifas.ufl.edu/in134.
I was recently sent some pictures of some unusual growths on pecan tree leaves. At first glance, the growths reminded me of the galls caused by small wasps that lay their eggs on oak leaves. However, after a little searching it became apparent this wasn’t the case. These galls were caused by the feeding of an aphid-like insect known as phylloxera.
Leaf galls caused by pecan phylloxera. Photo Credit: Matt Lollar, University of Florida/IFAS Extension – Santa Rosa County
The feeding from the phylloxera causes the young leaf tissue to become distorted and form a gall that encloses this female insect called a “stem mother”. These insects are rarely seen, but the hatch from over-wintering eggs in March/April just after budbreak. Once hatched, these “stem mothers” crawl to the new leaves and begin feeding. Once the gall forms, they start to lay eggs inside the gall. The eggs hatch inside the gall and the young phylloxera begin to feed inside the gall and the gall enlarges. The matured insects break out of the gall in May and some will crawl to new spots on the leaves to feed and produce more galls.
Pecan stem damage from phylloxera. Photo Credit: University of Georgia
There are two common species of phylloxera that infect the leaves. The Pecan Leaf Phylloxera seems to prefer young trees and the Southern Pecan Leaf Phylloxera prefers older trees. The damage from each of these insects is nearly indistinguishable. Damage from these insects is usually not severe and merely an aesthetic issue.
Once the damage is discovered on a tree, it is too late to control the current year’s infestation. There are currently no effective methods for control of phylloxera in home gardens. Soil drench applications witha product containing imidacloprid have been limited in their effectiveness.
Spring has arrived and so have the insects. Caterpillars are crawling around and one possesses a unique appetite.
Neodiprion spp. is the most common defoliating insect group affecting pine trees. In all, there are 35 species that are native to the U.S. and Canada. The redheaded pine sawfly, Neodiprion lecontei, is the primary species found in the Florida Panhandle.
Adult sawflies can be as large as 1/3 of an inch in length. The female can be two-thirds larger than the male and are mostly black with a reddish-brown head, with occasional white coloration on the sides of the abdomen.
Mature larvae of the redheaded pine sawfly. Credit: Patty Dunlap, Gulf County Master Gardener.
The ovipositor, the tube-like organ used for laying eggs, is saw-like, hence the common name. During the fall, females make slits in pine needles and deposit individual eggs, up to 120 eggs at a time. The eggs are shiny, translucent and white-hued. Mature larvae (caterpillars), as seen in the accompanying photo, are yellow-green, emerge in the spring and feast on pine needles. After weeks of feeding on needles, the mature larvae drop to the ground. The cocoon, a reddish-brown, thin walled cylinder, is spun in the upper layer of the soil horizon or in the leaf litter; this is called the pupae stage. The pupae overwinter, and adults emerge from the cocoon in the spring of the following year.
Mature larvae are attracted to young, open growing pine stands. Pine is the preferred host, but cedar and fir, where native, are secondary food sources. Neodiprion lecontei is an important defoliator of commercially grown pine, as the preferred feeding conditions for sawfly larvae are enhanced in monocultures of shortleaf, loblolly, and slash pine, all of which are commonly cultivated in the southern United States. Defoliation can kill or slow the growth of pine trees as well as predispose trees to other insects or disease.
Are there control methods? Yes, biological control is a major factor, as natural enemies are numerous. Disease, viruses and predators help regulate population control. For small scale control, physically removing eggs or larvae is key. Again, most infestations occur on younger tree plantings, so they’ll be in reach. Be sure to scout young pines for signs of infestation. Horticultural soaps and oils are effective chemical controls, if needed.
For more information, contact your local county extension office.
Supporting information for this article can be found in the UF/IFAS Extension EDIS publication, “Redheaded Pine Sawfly Neodiprion lecontei” by Sara DeBerry: https://edis.ifas.ufl.edu/pdffiles/IN/IN88200.pdf
UF/IFAS Extension is an Equal Opportunity Institution.