slide 0 of 00 Our Foe, The Pest: The reason you are here is because you have decided to use pesticides. You have decided to use pesticides as a tool to control pests. Pests come in all shapes and sizes. This presentation will cover some of the information regarding the three major pests we deal with. Insects, weeds, and diseases. Having knowledge of the pests we deal with can help with devising their control. Let s start with insects. slide 1 of 00 slide 2 of 00 Insect Damage: Most insects do not have any impact on our crops, some insects aid in controlling pest insects but it is the ones that are pests that we have to control. Insects cause damage to our crops and ornamental plants in a variety of ways. They chew on plant parts; tunnel or live in roots, stems and leaves; they suck on plant juices; cause galls; inject toxins; transmit diseases; feed on livestock; damage the products of livestock and feed on stored products. Insects vs Arachnids Insects and their relatives belong to a group called arthropods. Arthropods are all invertebrates, meaning they don t have a backbone. The structure that supports the arthropod s body is on the outside of their bodies very unlike our skeleton which is on the inside, insects are said to have exoskeletons. slide 4 of 45 Although there are many different groups of arthropods let us look at two such groups, the insects and the arachnids. In a comparison of these two groups we will find that insects have three body regions: the head, thorax and abdomen. Arachnids have two body regions: the head and an abdomen. 1 P age
Insect vs Arachnids: Insects have three pairs of legs attached to thorax and arachnids have four pairs of legs. slide 5 of 45 Insect vs Arachnids: Insects usually have 1 or 2 pairs of wings. Arachnids do not have wings. Good, flying spiders and ticks might put me over the top. slide 6 of 45 slide 7 of 45 Insect Development: Insects go through two major types of development. Leafhoppers, aphids, plant bugs and grasshoppers go through simple or incomplete metamorphosis. The young look and act the same as the adults. Hence control measures are often the same for each stage. In contrast, weevils, beetles, and moths go through complete metamorphosis. In complete metamorphosis, the young look and act completely different than the adults. Therefore the impacts and control measures would be different between the two developmental stages. Let s break these down into lifecycles. Insect Development: In simple metamorphosis the insect starts with an egg, then several stages of nymphs and finally the adult. There can be several stages of the nymph, each called a instar. In complete metamorphosis we also start with an egg then go through a number of larval stages, then a pupa and finally the adult. Control measures are usually most effective in the early larval and nymph stages. 8 of 00 2 P age
Feeding Type = Damage: The type of mouth parts an insect has will determine the type of injury we see. Insects with chewing parts produce notches and holes in the plant. Yet some insects have piercing sucking mouthparts. These insects will produce chlorotic or mottled looking leaves. How an insect feeds can impact the types of insecticide to use. An insecticide that merely coats the leaf may not be as nearly effective with an insect that has piercing sucking mouth parts as with one that chews. 9 of 00 Compete for: Farmers spend more money on weed control than any other pest. Weeds compete for water, nutrients, sunlight and reduce the quality of harvested products. In Wisconsin the weeds lambsquarter, velvetleaf, and giant ragweed name but a few of the weeds we deal with. 10 of 00 11 of 00 Life Cycles: Plants and thus weeds have three main types of life cycles. The first, are weeds that germinate, grow, flower, produce seed and die in one year. Their whole life cycle last one growing season. These are called annuals. There are summer annuals and winter annuals. As the name would suggest, summer annuals germinate in the spring live over the summer months and die in the fall. Winter annuals germinate in the late summer or fall, over winter and die in the spring. Examples are these are giant ragweed and lambsquarter. Biennials are plants live over two years. They typically, germinate and form a rosette in the first years growth, over winter then bolt in the spring, flower, produce seed and die in the second year. Examples of these are shepherd s purse and musk thistle. Perennials are plants that live over more than two years. These plants also germinate from a seed to start with then build complex structures to survived for several years. Weed scientists break perennial weeds into simple, like dandelion and creeping perennial weeds, like Canada thistle. The differences between these two are simple perennials have simple tap roots that typically do not lead to other plants. If chopped up, for instance in tillage, they can form new plants. Creeping perennials have vegetative reproductive parts such as rhizomes, stolons, and tubers. These structures all let the creeping perennial form new plants from these often forming large colonies as seen in Canada thistle. 3 P age
Contact vs Systemic Herbicide: Perennials can be difficult to control because they have underground structures that store reserves and can become new plants. Herbicides can be divided into two groups: the contact and the systemic herbicides. 12 of 00 13 of 00 Contact vs Systemic Herbicide: Contact herbicides damage weeds at the point of contact, killing shoots when they come in contact with the herbicide. However, systemic herbicides can move through the plant. Contact herbicides are less effective when controlling perennials. When dealing with perennials it is most effective when you can kill the underground structures. If you don t, the perennial will often resprout. In the case of the culprit Canada thistle, if you mow or burn off the top of the plant, where you may have had one plant, you will get more. Canada thistle will resprout sending shoots up to assure its survival. Life Cycle and Control: Generally, the optimum time to control annual weeds is when they are small in the seedling stage. However, like many annuals, they may be flush weeds. A new crop of them every time it rains, so a game begins where we try to get as many of these flushes without losing control of the too large annual. In the case of lambsquarter, it might be best to look to a preemergent herbicide. 14 of 00 The best time to go after biennials is in its first year of growth. Typically in the rosette stage. The spring before it bolts can be effective with some species. As mentioned above, controlling the underground portions of the perennial is essential. To do this you have to get the herbicide into those parts. One way in which this can be done is have your systemic herbicide follow the flow of sugars into these underground parts. Glyphosate tends to do this. Catching the perennial at a time when this is occurring would optimize the process. In many perennials, the fall is the time this occurs. 4 P age
Crop Injury: Herbicides kill plants. In a way it is amazing that they don t do the same to our crops. Yet on occasion we can get injury on our crops with herbicides that are labeled in those crops. 15 of 00 Crop Injury: Herbicides labeled in crops are often metabolized in the crop turning a potentially damaging herbicide into something that won t hurt the crop. However, detoxifying a herbicide in our crop takes resources from the plant itself and if the plant needs those resources to survive other problems, such as cold growing conditions, nutrient issues, drift from other herbicides and increased rates due to overlap or poor calibration. Crop Injury: Eventually the crop s ability or mechanism to overcome this becomes over taxed and we see a crop response. Plant Disease: A plant disease is an abnormality in the structure and/or function of the host plant cells and/or tissue as a result of a continuous irritation caused by a pathogenic agent or an environmental factor. In short something is throwing a monkey wrench into the plants physiology. This can be caused either by abiotic factors, such as nutritional issues, compaction, or too much water to name a few, or it can be caused by biotic factors as in the case of a causal agent or pathogen. Since we are talking about pesticides we will focus on causal agents or pathogens. 5 P age
Pathogens Cause Disease: Pathogens are the organisms such as bacteria, fungi, nematodes and viruses that induce disease in crops. Once a pathogen infects and develops within a plant, it is out of reach of most pesticides used in disease control. Therefore, pesticides are typically applied as protectants; that is, they are used to prevent infection from occurring in the first place. A few systemic fungicides, called eradicants, can control fungi even after infection has occurred. However, before a disease can take off or have serious impacts there are several things that have to be working in unison. The Disease Pyramid: The disease pyramid is a diagram of the four things that have to line up to induce enough disease to result in significant injury. When considering a disease such as Asian Soybean Rust two of the four factors are not present at the same time to induce large enough disease. The pathogen has to blow up in large enough amounts from the southern reaches of the US and thankfully, this had not happened early enough in the season to cause large impacts. Let s hope it stays that way. Let s take a look at the pathogens. Fungi: Fungi are plantlike microorganisms that cause such diseases as white mold of soybeans, corn leaf blights, rusts of small grains, and the potato late blight shown here. Fungal spores can be spread from diseased to healthy plants by wind, rain splash, insects, and farm equipment. Plant pathogenic fungi are also prevalent in the soil, so crop seed is often pretreated with fungicide to prevent some seed rots and seedling blights. Fungi penetrate plant tissue and either draw resources from the plant as a parasite or alter the plants physiology by producing toxins. Fungicides Protectants: Most fungicides are protectants. They form a protective barrier on the leaf s surface before the spores arrive that will either kill the spore or inhibit germination tube formation. A well timed fungicide application, shown here as the pink layer covering the leaf, will kill spores as they germinate, or prevent spore germination, and thus prevent infection. Because spores are microscopic, the spray must fully cover the leaf; even the smallest gap in coverage will provide a potential point of infection. Thus, apply fungicides at the full rate and volume although some fungicides recommend non ionic surfactants, using tickers are usually not recommended, which inhibit distribution of the fungicide. Note that as the crop plants grow, foliar applications of fungicides may need to be repeated periodically to protect newly emerged tissue. 6 P age
Fungicides Early Infection or Eradicants Most fungicides are protectants. They form a protective barrier on the leaf s surface before the spores arrive that will either kill the spore or inhibit germination tube formation. A well timed fungicide application, shown here as the pink layer covering the leaf, will kill spores as they germinate, or prevent spore germination, and thus prevent infection. Because spores are microscopic, the spray must fully cover the leaf; even the smallest gap in coverage will provide a potential point of infection. Thus, apply fungicides at the full rate and volume although some fungicides recommend non ionic surfactants, using tickers are usually not recommended, which inhibit distribution of the fungicide. Note that as the crop plants grow, foliar applications of fungicides may need to be repeated periodically to protect newly emerged tissue. Viruses: Viruses are little packs of DNA wrapped in a protein coat. They injure the plant by high jacking the plants cells and forcing them to create little copies of themselves. Viruses are unique in that there are no pesticides that directly control them. Instead, pesticides are used to control insect vectors; that is, insects that transmit viruses from one plant to another as they feed and weeds that may harbor viruses. Most insect vectors, such as aphids, have piercing sucking mouthparts, so systemic insecticides will often provide the best control. Rodents The last group of pests we will discuss are the vertebrates. Within this group, rats and mice cause the greatest damage. They eat and contaminate livestock feed and stored grain, transmit disease to people and livestock, and cause damage to buildings. Sanitation, which involves denying access by rodents to food, water, and harborages, is the key to preventing rodent problems. The control of rats and mice with a pesticide does not require any permits, but sometimes the pest in question is a deer or birds. To control animals other than rats and mice or to control birds with a pesticide a permit will be required from the DNR. Also, if you are using strychnine a permit will be required from DATCP. 7 P age
Rodenticide Baits: The use of rodenticide baits can be an effective way to control rats and mice. They introduce little pesticide into the environment and are placed only where the rodents encounter them. Now there are many different kinds of tamper resistant bait stations available on the market. These bait stations are designed for the specific species of rodent that you are trying to control and limit the possibility of poisoning non target animals. 8 P age