Garden Pests and Beneficial Insects
Season one of our very first garden was not very successful. The plants grew but the insects ate more than their fair share. I would never apply harmful chemical pesticides, so the army of invaders conqured the garden. I learned that there are three essential organic insect and disease products that every gardner must have on hand. Thuricide, organic garden oil spray (various types), and beneficial insects.
Most gardners treat for insects and plant disease far too often. This has the potential of killing beneficial insects and soil microbes. Most garden insects are beneficial or neutral. There are a number of resources with images on the web that will help you identify the insect or disease before you treat.
The main types of plant disease are Fungi, Bacteria and Viruses. Below are a few of the most common found in Florida. (Information and images courtesy of the University of Florida IFAS Extension office) If you live in a different climate, check with your local agricurtural university or county extension office for pests common to your area.
To help lessen the chance of disease do not over water and never water at night or so late in the day that the soil will not have time to dry out before nightfall. The plants need time to dry which helps prevent the spread of disease.
Bacterial Spot: One of the most common diseases of tomato in Florida is bacterial spot, a disease caused by the bacterium Xanthomonas vesicatoria or X. perforans. Bacterial spot is especially common in warm, rainy weather. All plant parts are affected, but the spots (lesions) on the leaves are most noticeable.
Dark brown leaf spots (lesions) appear as small (1/8 of an inch or so), wet-to-greasy areas on both upper and lower leaf surfaces. There may or may not be yellow halos around these spots. These lesions may run together to form rather large, blighted areas on leaves. It is not unusual for affected leaves to drop off plants prematurely.
Target Spot: Target spot is a fungal disease that has become increasingly important over the years on commercial tomato farms in Florida. This disease has become more prevalent in home gardens over the last several years, so it is a plant disease that homeowners should be aware of.
The causal fungus, Corynespora cassiicola, produces abundant spores that are readily dispersed on wind currents and may blow into gardens from remote locations.
On tomato leaves, the disease first appears as small, brown spots with light brown centers and darker brown margins. There can be yellow halos around these spots. Especially in early stages, target spot on the leaves is extremely difficult to differentiate from bacterial spot. Even experienced professionals can have difficulty telling these two diseases apart without laboratory tests. As the target spot disease develops, spots run together, and large blighted areas appear on leaves.
Fruit lesions caused by the target spot fungus are more distinct and easier to distinguish from bacterial spot than are lesions on leaves. At first, fruit symptoms appear as small, slightly sunken flecks. As the disease progresses, lesions become darker and deeper. These lesions may overlap, resulting in large, pitted areas. As fruit ripen, large sunken areas are evident, often with a gray or black growth of the fungus in the lesion center. Most home gardeners are reluctant to consume these damaged fruits.
Late Blight:Late blight is one of the most famous diseases in the history of agriculture. The causal fungus, Phytophthora infestans, was responsible for a devastating epidemic on potatoes in Ireland in the 1840s that led to widespread famine and starvation. The huge migration of Irish to North America was in great part a response to the impact of late blight on the most important crop in Ireland. Today, late blight is still a major concern to both potato and tomato growers on commercial farms in the United States.
We occasionally see late blight on garden tomatoes in Florida. The disease is usually associated with weather that is relatively cool (e.g., daytime highs in the 60s and lower 70s) and damp.
On tomato leaves, the symptoms of late blight initially consist of light brown to purplish spots that rapidly enlarge to purplish, blighted areas. Early in the morning and under wet conditions, a white growth of the fungus may be visible on the lower leaf surface. Stems may become infected, as well, with large purple to black sections that make stems look as if they were burned.
On infected tomato fruit, mahogany to purple blotches appear, sometimes in a ring pattern , and fruits often become overcome by a foul-smelling soft rot, as secondary bacteria follow the late blight infection.
Tomato Spotted Wilt: Tomato spotted wilt (TSW) is a viral disease. It is transported from diseased to healthy plants by thrips, an insect that commonly feeds inside many different types of flowers, including the blossoms of tomato.
The tomato spotted wilt virus (often abbreviated TSWV) has a wide host range, producing symptoms in at least 63 plants grown commercially in Florida. These include vegetables, field crops, and ornamentals. TSWV is of more concern in North Florida, presumably because the thrips species and weed hosts that are best adapted to the spread and survival of this virus are more abundant in the northern parts of the state. However, TSWV may occur in South Florida, too.
A wide range of symptoms can occur with TSWV. Small, light brown flecks first appear on leaves. These spots later turn brown followed by a general browning of leaves that die and appear drooped on stems. Brown to purple brown streaks form on stems. Plants are often stunted and, with the droopy leaves, appear wilted. Green fruit show concentric rings of yellow or brown alternating with the background green color. Striking brown rings occur on red-ripe fruit.
Tomato Yellow Leaf Curl Virus: This virus was first introduced into Florida in Miami-Dade County in 1997. It is a constant problem in commercial fields throughout Florida. We have observed it in gardens throughout southern Florida, especially in areas with significant commercial tomato production.
This virus is transmitted by a species of whitefly. Severe symptoms occur on tomato, especially when young plants are infected. Young, diseased plants are severely stunted. Leaf edges curl upward and appear mottled (i.e., show alternating areas of light and dark green). The tops of plants appear bushy. Often, fruit set is poor or nonexistent.
Control of TYLCV is difficult. Varieties with resistance to TYLCV are available at local garden centers and should be used, especially if you reside in areas with significant commercial tomato production. Susceptible varieties can be grown, but successful control of this virus begins with the purchase of TYLCV-free transplants. An isolated, infected tomato plant or two can be removed and destroyed in an effort to eliminate sources of virus that might infect other tomatoes. A lengthy period of time between plantings in the garden will help break the cycle that can lead to repeated virus infection. For example, in South Florida, it makes sense to have a tomato-free period in the garden for three to four months in the summer. (Tomatoes don't set fruit particularly well anyway during this time.) While the control of whiteflies is essential to prevent the virus from spreading from diseased to healthy tomato plants, this may not be practical in a home garden.
Bacterial Wilt: Bacterial wilt, caused by Ralstonia solanacearum, is a serious soilborne disease of many economically important crops, such as tomato, potato, tobacco, and geranium in the southeastern United States. R. solanacearum is an extremely complex and diverse bacterial species; it is pathogenic to several hundred plant species belonging to more than 50 families.
Although diseased plants can be found scattered in the field, bacterial wilt usually occurs in foci associated with water accumulation in lower areas. The initial symptom in mature plants under natural conditions is wilting of upper leaves on hot days followed by recovery throughout the evening and early hours of the morning. The wilted leaves maintain a green color and do not fall as disease progresses. Under favorable conditions, complete wilt will occur.
The vascular tissues in the lower stem of wilted plants show a dark brown discoloration. A cross section of the stem of a plant with bacterial wilt produces a white, milky strand (ooze) of bacterial cells in clear water. This feature distinguishes the wilt caused by the bacterium from that caused by fungal pathogens (e.g., Fusarium wilt).
Bacterial wilt is very difficult to control after it is established in the field. No single measure totally prevents losses caused by the disease. The race 1 strains of R. solanacearum have been found to cause significant losses in tomato, especially in North Florida and in other southeastern states.
Powerdy Mildew: Powdery mildew is a common and serious disease of cucurbit crops in Florida. This disease occurs in cucumbers, muskmelons, honeydew, squash, gourds, and pumpkins grown both in field and greenhouse conditions. Previously, powdery mildew was an occasional problem for watermelons, but for the past 5 years the incidence of powdery mildew outbreaks has increased. A powdery mildew infection acts as a sink for plant photosynthates causing reductions in plant growth, premature foliage loss, and consequently a reduction in yield. The yield loss is proportional to the severity of the disease and the length of time that plants have been infected. For instance, in cucumber there is a negative linear relationship between disease severity and yield (Dik and Albajes, 1999). If this disease is not controlled in a timely manner, symptoms can be severe enough to cause extensive premature defoliation of older leaves and wipe out the crop.
Symptoms of a powdery mildew are often easier to identify than symptoms of any other disease because powdery mildew forms obvious pads of whitish mycelium on upper and lower leaf surfaces, petioles, and stems. During the crop growing season, the fungus produces hyphae and asexual spores, called conidia, on leaves. This disease can be first noted on older leaves, which develop reddish-brown, small, restrained round spots. At this point, a microscopic examination is necessary in order to discern if typical conidia of powdery mildew are present. Later on, those spots become white as hyphae and spores are produced in abundance Infected areas enlarge and coalesce quickly, forming a white powdery mycelium that resembles talc. Severely infected leaves lose their normal dark green color, turn pale yellow and then brown, and finally shrivel, leaving cucurbit fruits exposed to sunburn.
Biorationals and Non-harmful Chemicals. Biorational materials with low toxicity for plants may have a role in disease management systems (Bélanger and Labbe 2002). These compounds do not cause phytotoxic symptoms; in many cases the mechanism by which disease supression occurs is unknown. Biorational compounds can be used to reduce incidence of infection by powdery mildew in cucurbit crops. Among these biorational materials: natural and mineral oils, peroxigens, cow's milk, silicon, and salts of monovalent cations such as sodium, potassium and ammonium may be used. When considering using these biorationals it is important to contact UF/IFAS Extension for additional information. For more information click HERE.
Harmful Nematodes: Nematodes are unsegmented roundworms, different from earthworms (http://edis.ifas.ufl.edu/in946) and other familiar worms that are segmented (annelids) or in some cases flattened and slimy (flatworms). Many kinds of nematodes are found in Florida soil. Most nematodes are beneficial, feeding on bacteria, fungi, or other microscopic organisms, and some may be used as biological control organisms to help manage important insect pests. However, plant-parasitic nematodes feed on live plants and are detrimental to the garden.
As plant-parasitic nematodes feed, they damage the root system and reduce the ability of a plant to obtain water and nutrients from the soil. When nematode numbers get high, and/or when environmental stresses occur, aboveground symptoms may become evident. Aboveground nematode symptoms often resemble nutrient deficiencies or drought stress. Symptoms include yellowing, wilting, and stunting.
The bionematicide MeloCon WG contains a fungus that parasitizes nematode eggs. Results from University of Florida trials indicate that MeloCon can suppress but not eliminate root-knot and sting nematodes. When purchasing MeloCon, have it delivered directly to you from the manufacturer, and keep it frozen until it is used. To apply, mix MeloCon with water, and then either drench the planting bed with it or spray it onto the planting bed and irrigate. MeloCon works best when it is administered in multiple applications, starting before transplanting and continuing through the growing season. It is generally not effective when used to treat established plants after they have been damaged by nematodes. For more information click HERE
HARMFUL INSECTS: In our garden we have experienced two main types of harmful insects.
The first is leaf and fruit eating worms. Most of these types of worms are controlled with an application of Thuracide. Thuricide Concentrate is a biological insecticide with Bacillus thuringiensis (Bt). Thuracide and organic treatment that is specific to certain worm pest insects can be used with Beneficial Nematodes. It has no or very low impact on non-target organisms, human, beneficial insects, birds, fish and wildlife. Bt works by disrupting the insects' digestive system which causes starvation and death. Crops can be harvested the day after Bt is applied. This stuff really works. It is available at most big box stores. If you have a large garden you may want to but the product in bulk. The product we us is DiPel. Click HERE for more information.
The second major pests are soft body leaf sucking insects which include aphids, white flies and leaf miners to name a few. There are a number of organic products that can control these harmful critters. Some of the products include Neem Oil, 3-in-1 spray, Wetable Sulphur, BotaniGard(R), Insecticidal Soap. For a complete list of options click HERE.
This WEBSITE is very helpful in identifying pest and suggesting a solution. It includes images to help you identify the pest.
We use beneficial predators and parasites, beneficial nematodes, and beneficial organisms in our garden to help control the unwanted guest in our garden.
Beneficial Insects do not harm people, plants or pets they should be released when past densities are low. But beneficial insects are not a miracle cure; it can take some time before they start to resolve a problem. We have released ladybird beetles, green lacewing, and praying mantis egg cases. There are other beneficial insects to consider, click HERE for a list or to order.
Beneficial Nematodes are parasitic to insect pest that typically have a larval or pupal stage life in the soil. They have also been shown to affect aboveground stages of adults, nymphs and larvae. They can control a wide variety of garden pest but can also help control fleas ants and termites text and more. We apply a combination of three different types of beneficial nematodes. Click HERE for more information or to order.
Beneficial Organisms can come from any of the microscopic groups of organisms many of which are vital to soil health. For example types of fungi and bacteria help to decompose organic matter releasing nutrients.
Mycorrhizae, which literally means "fungus and root", are fungi that have developed a symbiotic relationship with root systems of living plants. The specialized fungi colonize plant roots and extend deep into the soil. These fungi will form on the roots of plants naturally if organic techniques and products are used but it can take some time. To speed up the process there are products available that can be applied. We use a product named MycoGrowTM. You should only have to apply this product one time. Click HERE for more information. This is also a good product, it includes 11 species of beneficial fungi and 15 beneficial bacteria.Click HERE