Friday, August 27, 2010

Help, my plants are drowning!

Wow, have we seen a lot of rain over the last week. Many parts of Pinellas County are completely saturated and some are dealing with standing water. Many plants in the landscape are not tolerant of standing water. Under these conditions the roots are unable to get oxygen and essentially the root system suffocates. Some plants can tolerate up to a week or so in these flooded conditions while others will be damaged after only a day or two. Recovery from this situation is just as varied, as some plants will recover in just one growing season while others may decline and die. Healthy established plants will generally fare better than older stressed plants and young seedlings. Here are some of the symptoms that you might see above-ground if your plants have root damage from standing water:

-leaf yellowing or browning
-droopy foliage
-leaf drop
-leaf and stem wilting
-stem and limb die-back
-plant death
The landscape showing signs of root damage due to flooding.

There are some things you can do after this occurs to lessen the damage to some plants. If you have container plants that have been flooded put them up on blocks, bricks, gravel, etc. to allow the drainage of excess water. Due to erosion you may have sediment, mulch, etc. deposited on your plants after the water recedes. Carefully remove this sediment so as not to harm the roots. You may also have exposed tree roots where the soil was washed away. These roots should be covered with soil to protect them. Try to return the soil to its original depth/condition, as putting too much soil on the roots will also reduce the oxygen available to them. The goal is to return to pre-flood conditions as soon as possible. Furthermore, according to the University of Florida, “trees showing signs of flooding stress should have up to ½ the leafy tree canopy removed to reduce the stress imposed by soil conditions. Reducing the size of the canopy will improve the chances for tree survival”. It is recommended that you consult an arborist for this activity.

Wet soils are also favorable for a number of soil-borne root and crown rots including Fusarium spp. and Phytophthora spp. These organisms are responsible for a number of root and crown rots that are potentially fatal. Keep a watchful eye on your landscape after flooding for symptoms that often look similar to drought stress like wilting or a dull appearance to leaves. Contact Extension if you suspect these infections as there are different control and sanitation methods that may help manage the spread of the organisms. Different plant species and root and crown rot species call for different responses that would be too numerous to explore here. So, keep an eye on your landscape and an umbrella at the ready!

Leaf discoloration due to leaf and crown rot in Liriope muscari.

Disclaimer: This post only addresses freshwater flood impacts. Salt water flooding brings with it a host of other issues too numerous to address in this post.

Friday, August 20, 2010

Avocado Lace Bug

The avocado lace bug (Pseudacysta perseae) is a pest that has become increasingly significant to avocado plants since the early 1990s. The avocado (Persea americana) is the main host for this pest in Southern coastal Florida. The avocado lace bug does damage to avocado leaves with its piercing-sucking mouthparts. This pest attacks the underside of the leaves where it feeds by extracting chlorophyll and other plant fluids. This causes destruction of plant cells and leads to the chlorotic and necrotic damage you see in the photos below. When looking at a tree with this pest you may observe leaves that look brown and “scorched”.

The avocado lace bug is a very small pest- only about 2mm as an adult. This can make it difficult to see the insect, but you can see them on the photo of the underside of the leaf- they look like little black specks. It may be easier to see them using a hand lens or you can shake an infested branch over a sheet of white paper. They will be easier to spot and identify on the paper than on the leaf. Here is a close-up of the avocado lace bug:

The adults are the larger ones with the “lacy” wings on the left and the nymphs are the smaller black insects on the right. The black oily-looking specks are the eggs.

If there is a large infestation of avocado lace bugs it may result in some defoliation, and the resulting damage from the pest can become an opening for the introduction of infections. If you discover that your avocado has this pest there are a few controls at your disposal. A strong jet of water will dislodge them from the plant, but may not kill them. This is probably most effective if the infestation is minor. Insecticidal soaps or horticultural oils are effective controls if they are applied directly to the insects. Monitoring for this pest in the future will be necessary and the treatment will need to be repeated as necessary according to the label. Of course, the mechanical control using the jet of water can be used anytime.

Click here for more information:

Thursday, August 12, 2010

Tropical Sod Webworms

There are several pests that affect lawns in Florida. (Don’t we know it?) Here we will highlight a particular lawn caterpillar called tropical sod webworm (Herpetogramma phaeopteralis). Tropical sod webworm is an insect that undergoes complete metamorphosis. They have an egg stage, larval stage (several), pupal stage, and adult stage. The most damaging stage of the tropical sod webworm is the larval stage, which we all know as the caterpillar. A mature tropical sod webworm is about ¾”-1” long and is grayish-green in color. The more of your grass they have eaten- the greener they may appear.

Two tropical sod webworm caterpillars. The curled position at center is how you might find them resting during the day in your lawn.

Their turfgrasses of choice include St. Augustinegrass, bermudagrass, and zoysiagrass. They are most active in our area from spring through fall, but can be found year-round in South Florida. They feed on the grass blades and can cause a “ragged” appearance to the blades. If you have tropical sod webworm you may notice a thinning of leaf density and eventually brown patchy areas in the lawn. Tropical sod webworm larvae feed at night and can usually be found during the day coiled up at the soil surface. The presence of the moth (adult stage) is another sign of their existence. These moths lay their eggs on the grass blades and are active mainly from dusk until dawn. Click here for more information on tropical sod webworm and control methods.

The moth (adult stage) of the tropical sod webworm.

A properly maintained lawn can reduce the susceptibility of your turfgrass to these insects. Some of the practices that can strengthen your lawn include: proper mowing height for your turfgrass species, proper irrigation practices, and proper fertilization. Too much nitrogen can cause rapid leaf growth, which in turn increases your odds of caterpillar problems. Click here for more information on proper turfgrass maintenance.

Click here to watch an informative YouTube video on tropical sod webworms by Doug Caldwell, Ph.D., the Commercial Landscape Horticulture Extension Agent in Collier County, FL.

Thursday, August 5, 2010

Mole Cricket Hunters

Mole cricket, photo courtesy of Texas A&M Univ.

Summer is in full swing! It’s hot, rainy, and plants are growing. All of that tasty succulent growth is like a buffet for a wide array of lawn and garden pests. In the coming weeks you may discover that your lawn has mole crickets. Mole crickets are especially troublesome in bahiagrass lawns, but will damage other types of turfgrass. There are three species of mole crickets found in Florida: the shortwinged mole cricket, Scapteriscus abbreviatus; the southern mole cricket, Scapteriscus borellii; and the tawny mole cricket, Scapteriscus vicinus. Mole crickets are adept at digging and as they tunnel through the ground they sever grass roots. They eat both the roots and shoots of grass and will leave unsightly brown patches in your lawn and sometimes cause the earth to bulge up. To add insult to injury (literally) they are considered a tasty treat by raccoons and armadillos that may dig up your lawn for a mole cricket snack.

Mole cricket damage

There is an easy way to find out if you have these little diggers. Simply mix up a concoction of 1.5 ounces of liquid dishwashing soap in 2 gallons of water. Sprinkle this mixture over 4 square feet if your turf. If 2-4 mole crickets appear within three minutes of the application then you may consider a control program. There are several controls listed in the link below called “Pest Mole Cricket Management”, but I would like to focus on a particularly interesting method using “Mole Cricket Hunters” aka the Larra wasp, as a biocontrol.

Biocontrol is quite simply the use of a beneficial insect to control a pest insect. In the case of mole crickets there is a parasitic wasp called the Larra wasp (Larra bicolor) that will attack all three species of mole cricket here in Florida. (To learn more about the way they attack and kill mole crickets please see the last link below.) The Larra wasps do not sting humans unless you try to catch one and hold it in your hand. But why would anyone do a silly thing like that? They are already present in at least 31 Florida counties, including ours, so all you have to do is encourage them to frequent your landscape. How can you do that? It’s easy: plant host plants that the wasps obtain nectar from. The two most popular choices are shrubby false buttonweed (Spermacoce verticillata) and partridge pea (Chamaecrista fasciculata). They are both Florida native wildflowers and require very little assistance to grow and thrive. The University of Florida’s entomology department recommends planting these before you have a mole cricket problem, but there’s no time like the present to employ an environmentally friendly control like this! For more information please see the following links:

Mole Crickets

Pest Mole Cricket Management

Mole Cricket Hunters