Non Chemical Management


*Text adapted after S. Newman and L.P. Pottorff *Colorado University and Jefferson University

*With the increasing concern about use and misuse of pesticides in commercial agriculture and home gardens, there are more and more inquiries for organically grown commodities every year.

Non chemical control practices for plant diseases have been known and recommended for years. Any integrated pest control program must always include cultural and sanitation practices, two important components of non chemical disease control.

Unfortunately, disease problems may begin as soon as seeds are planted and can continue into harvest and storage. Plant diseases may be caused by several pathogenic organisms, such as fungi, bacteria, viruses, mycoplasmas and nematodes. In addition, nonliving factors, such as deficiencies or excesses of water, light, temperature, air pollution, pesticides and nutrients, can either predispose a plant to disease or directly cause plant injury.

Fortunately, many disease problems can be prevented or controlled without pesticides. Effective plant disease control begins at the onset of disease or even before symptoms appear.

In the below link S. Newman and L.P. Pottorff are listing ways to control plant diseases without chemical, the items below are presented

– Prefer disease resistant potato Variety

– Exclusion

– Eradication of disease

– Sanitation

– Crop Rotation

– Soil Sanitation Treatments

– Cultural Management


(G.Forbes, W. Perez, Potato Late Blight, Technichal Manual, CIp’s collection)

Cultural control involves all the activities carried out during agronomic management which alter the microclimate, host condition and pathogen behavior in such a way that they avoid or reduce pathogen activity.

Planting time: Schedule planting time, especially in places where planting is made under irrigation, to avoid the period of higher incidence of the disease. This is not always possible in continuous production areas.

Selection of crop fields: Soils must have good drainage and adequate aeration, in order to avoid moisture on foliage and ground. Those areas remaining wet due to excessive soil moisture or excessive shading are potential sources for incidence of late blight. Some traditional techniques as “huacho rozado” in Colombia and Ecuador, which apparently improve drainage and aeration, have been associated with reduction of late blight (Unpub-lished data).

Destruction of volunteer plants and weeds: Avoid potato monocropping to escape primary inoculum likely to be present in plants or tuber debris infected during the previous season. Destroy any other alternative host, not only for infestans but for other diseases and pests.

Selection of variety:It is advisable to use resistant varieties. Combining varieties should be avoided in order to achieve adequate agronomic management of the crop and better disease control. Nevertheless, some authors recommend the mixture of varieties to reduce disease severity and obtain adequate yields, particularly the combination of susceptible and resistant varieties.

Selection of seed: Use of healthy seed tubers for planting must be guaranteed. Sometimes seed can be infected with infestans without blight symptoms. So far, there is no evidence that infected seed can be “cleaned” or healed with fungicides. However, there is a risk that infected tubers will sporulate and contaminate more tubers during the storage process or transportation. This is particularly problematic in countries where seeds are cut. In case contamination is likely to occur, it is possible to avoid an increase by treating seed with an effective product against P. infestans (See fungicide table).

Distance between plants and between rows: Distance between plants and between planting rows must be appropriate to reduce moisture on the foliage. This practice should be related to the variety and purpose of the crop (seed or consumer potato). However, data generated about the effects of plant density on late blight incidence are not consistent and often farmers must make density decisions based on other demands.

Hilling: Make high, well-formed hills to avoid or reduce contact of tubers with sporangia or zoospores coming from infected foliage. Hilling high has also been related to less severity of blight on foliage, because it promotes better drainage and aeration of soil causing foliage to dry faster.

Plant nutrition: Some authors have reported that high doses of phosphorus and potassium reduce late blight whereas high doses of nitrogen increase its incidence. Phosphorus and nitrogen apparently have contrary effects on tuber blight. Nitrogen slows down tuber maturity, which favors blight appearance, while phosphorus reduces incidence, accelerating maturity. A recent investigation in the Andean region proved that fertilization effects on late blight were less than effects of fertilization on yield so farmers generally make fertilization decisions based on yield.

Foliage cutting: Fifteen days before harvesting, foliage should be cut and removed from the field. In some countries, desiccants (sulfuric acid) or an herbicide (for example, DIQUAT) is used. Nonetheless, sulfuric acid is very dangerous and Diquat may damage tubers under certain conditions. It seems that several tuber diseases are favored when stem and root tissues rot. Therefore, “green lifting” (or “green harvest”) has been studied in the Netherlands; it consists of harvesting the tubers and putting them back in the soil, without any stem or roots. Based on this investigation, we could suppose that uprooting the plant (instead of cutting it at soil level), would be favorable but no studies on this topic are known. Because of its simplicity and efficacy, It seems that cutting foliage with a machete is generally recommended for small farmers, because it reduces late blight incidence in tubers due to early removal or destruction of plant foliage prior to harvesting.

Irrigation: Avoid excessive furrow irrigation, especially in soils with deficient drainage, because it may create microclimates that favor disease or tuber rot. In places where sprinkler irrigation is used, do not irrigate in the evening as leaves will remain wet for a longer period of time and will favor foliage infection, exposing tubers to a potential infection.

Sanitation: In those areas where the disease is sporadic or limited to few sources of infection, desiccants should be applied to eliminate initial sources of inoculum, in order to prevent pathogen, spread. Infected leaves can be easily removed from small plots or gardens.

Timely harvest: Harvest in a timely fashion and avoid field work under humid conditions, which favor tuber infection and further disease spread.

Destruction of discarded tubers: After harvesting, it is recommended to pick up discarded tubers (rotting, damaged, etc.) and use them to feed pigs or, lacking that, they should be otherwise discarded (composting or burying) to avoid their becoming a source of primary inoculum or a reserve for other pests and diseases.

Appropriate storage: Healthy tubers must be stored in order to avoid infections during the storage period. The use of diffused light stores is recommended. The use of seed tubers with green sprouts coming from these stores may result in a more uniform crop which can be harvested earlier, thus reducing exposure time to late blight.