Växtskyddsteknik för ekologisk frukt- och bärodling - skadedjursbekämpning med fysikaliskt verkande bekämpningsmedel

Pesticides with a physical mode of action, as opposed to those with a chemical action, have a real scope in organic production, when preventive means no longer are sufficient. Further on, they have opportunities to supplement the conventional chemical plant protection products and are especially interesting for future situations with priority on integrated pest manage-ment. The physically-acting pesticides are often based on substances, categorized as food or household chemicals and are therefore assumed to result in less risk to health and safety, resi-dues and the surrounding environment. However, this has not always been studied in detail. These pesticides are by nature strictly contact-acting and require a thorough spray liquid coverage to obtain the wanted biological effect. The knowledge of adequate application tech-nology is limited, as well as, in general, the possibilities for the use of this kind of plant pro¬tec-tion products against pests in horticulture. The objectives of the project are, based on applied research, to produce knowledge of physic-cally-acting pesticides and of suitable application technology for these, within fruit and berry production. Mineral oils are the most studied and developed of the physically-acting substances. They are now carefully graded for chemical purity and use. The earlier understanding of their suffo-cating mode of action has been supplemented with new research, revealing that their modes of action against pests are several, including a chemical effect on the nerve system. It was also assumed that vegetable oils and soaps have the same mode of action, but it is still not thoroughly investigated. So far, the hypothesis is that they are suffocating and have skin dissolving effects, partially confirmed in various research. Soaps and vegetable oils contain, depending on their plant origin, different composition of fatty acids. As different fatty acids are considered to be different efficient, this could indicate that some plants are more suitable as raw material sources. Canola oil, with a high content of oleic acid is an interesting product in this context. No resistance reactions are noted in the use of physically-acting agents, most probably because several different modes of action are combined, including some strictly physical. Field trials with the oils resulted often in a good effect, on conditions that the treatment was repeated several times during the season (example: canola oil against the raspberry beetle in field raspberries), or made with high liquid volume rates (canola oil against the fruit tree red spider mite in greenhouse raspberries), or if mineral oil was used (mineral oil against the fruit tree red spider mite in apples). In laboratory trials full mortality was obtained if apple shoots, infected with eggs of the fruit tree red spider mite, were dipped in spray liquid with canola oil, underlining the importance of application, even though recent research shows that ‘dipping’ implies change of the physical conditions for the penetration of the organism. In any case, a high deposition is needed to get the required effect. Laboratory experiments with fully exposed green peach aphids showed that coverage of 90 % (measured by using water sensitive paper) only gave a mortality rate of about 20 %. If the same treatment was repeated immediately, 70 % mortality could be reached. It is extremely difficult to achieve these coverage or deposition levels in crops with fully developed foliage. In the most difficult located positions (leaf underside in the center of the canopy), it is difficult to reach above 10 – 15 % coverage. Beneficial fauna is most probably affected by physically-acting pesticides through the same modes of actions as pests. However, we have not seen any serious adverse effects, which is well in line with other research. An important part of a reasonable explanation is that bene¬ficial fauna and pests are rarely simultaneously in the same development stage. To get a good effect of the physically acting pesticides, it is most important to choose the right treatment ‘spray window’, when pests are exposed to the spray and are at a sensitive stage. Generally, conditions are good if the treatment could be carried out before the leaves are put out. Our good results against the fruit tree red spider mites were obtained early in the season, with virtually naked trees or plants, with the mite eggs relatively well exposed. There are documented risks of leaf damage from oils and soaps. Treatment before leaf bloom is therefore an advantage. In our experiments, we saw no tendencies of damage. It should be noted that spraying with oil and soap also has a deterrent effect on both oviposition and fee-ding. This factor has not been investigated in the project. It can be stated that the modes of action for vegetable oils is not clear. Therefore, further research of a more basic nature could focus, for example, on canola oil and its impact on pests in different stages. The more practically oriented results of this project are obtained by study-ing the influence of coverage on efficiency. Methods were developed, which makes it possible to examine more species, stages, concentrations and substances. Other important fields of knowledge, concerning the conditions in practical horticulture in relation to efficiency, could be studied through a series of student theses, based on collection of field data, such as the plant protection situation, application method, dosage and results. The main contribution to the knowledge of the use of physically-acting pesticides could be summarized as follows: • Physically-acting pesticides provide in most cases an effect against pests. Canola oil in many cases results in a good effect, but mineral oils are even better • The effect of vegetable oils and soaps are poorly investigated, but probably dominated by anoxia and dissolving of the skin. The mineral oil modes of action also include nerve affecting chemical modes • No resistance symptoms developed through use of physical acting pesticides • Beneficial fauna is affected only to a limited extent, probably because their sensitive stages of development do not occur simultaneously as pests • Modern, high-quality application equipment and technology is needed, and often in combination with high liquid rates • It is very difficult, if not impossible, to achieve a good penetration and high depo-sition in dense horticultural canopies without air assisted spray equipment • It is very important to make the treatment when the pest is most sensitive and most exposed.