Weeding
Remove unwanted plants from your field. Volunteer crops and weeds compete for nutrients, water, light and space with potatoes in the field. Remove them as soon as they germinate in order to curb yield losses associated with their presence.
All volunteer plants and off type crops should be weeded out.
Off type plants - These are plants that grow among the crops planted on the farm but may not have been the targeted crop. They sprout from the seeds used and may be of different varieties or deformed plants. To ensure uniformity, these plants should be uprooted and destroyed as soon as they are spotted in the field.
Volunteer plants -These are potato plants, which grow from tubers that remained in the field from the previous crop after harvesting. These plants will grow among your crop and may host pests and diseases. They therefore need to be removed preferably before the target crop emerges to reduce chances of pests and disease infestations and spread.
Advantages of weeding your Irish potato farm
• Reduces competition for nutrients, light, moisture and space.
• Alternate hosts for pests and diseases are eliminated.
• Conditions for disease build up will not be favorable hence you will use pesticides and Fungicides less frequently.
Steps and methods of weed management
1. Prepare to weed 2 weeks after crop emergence or on appearance of weeds so that you reduce damages to the potato crop.
2. To weed, rogue or uproot weeds as they grow or use hand tools to uproot.
3. Spray weeds with selective herbicides in situations where labor is not available or is expensive. However, ensure you get assistance from experts on herbicide selection, its mode of action, application timing and application protocol and techniques.
4. Weeding is done again after two weeks; in case new weeds will have germinated.
When using a hoe to remove weeds, care is taken not to damage the tips of the stolons which may have grown out to near edges of the ridge.
5. No weeding is done again once the crop canopy has covered the ground because a few weeds will grow when the inter row is covered.
Walking through a mature crop will damage the leaves and stems and risk spreading Virus X from infected to healthy plants.
Potato Diseases and Pest Management
Potato pests and diseases result in high yield losses both in the field and during storage. The potato diseases are caused by fungi, bacteria or viruses. These diseases, especially late blight, are as a result of pathogens spreading faster in cold weather conditions. Each of these fungal pathogens is discussed in detail below.
1. Potato Late Blight
Late blight is caused by an oomycete (water mold) Phytophthora infestans and is the most common disease of potatoes.
Soft rot of tubers is often observed in the store when a potato field is infected with late blight. The disease damages the leaves, stems and tubers and can wipe out a potato crop in a short period of time in less than two weeks after disease establishment.
Symptoms
Early symptoms are small pale to dark green spots appearing on underside of leaves, symptoms spread later to the stem and tubers.
Round, dark brown watery looking blotches appear on the underside of potato leaves. The blotches appear wet and irregular at the margins; the blotches appear brown when dry and black when wet. Sometimes these blotches can be surrounded by a yellowish green ring and may extend to the tip of the leaf. Also on the margin of these lesions, a white mildew like (fuzzy or cottony growth) appears. This white growth is due to the presence of microscopic structures called sporangia, which are formed on sporangiophores.
After sporulation these sporangia are carried by wind currents, rain splashes etc. to previously healthy leaves and plants, where the infection cycle recommences.
Symptoms on the stem are dry, dark brown elongated blotches. With severe infections, these blotches may encircle the stem, causing it to break at the location of the blotch. Infected stem wilts and dries.
On tubers, light brown blotches that are slightly sunken may appear on the surface. Dry, light brown blotches, having a granular texture, may be seen under the skin when the tubers are cut into sections. Tubers with late blight symptoms do not produce bad odor unless they are subjected to a secondary infection by bacterial soft rots.
Late blight symptoms can be confused with symptoms of early blight, frostbite and Septoria leaf spots. The key indicator of late blight infection is the white downy growth on the underside of the leaf. Early blight lesions are confined to areas between the leaf veins whereas late blight lesions.
Signs
The signs of the causal agent are white fuzz around the grey blotch on the underside of the leaves. The white fuzz is caused by the spores of the causal agent being held by a thin thread.
Transmission
The Phytophthora infestans life cycle may last between three and fifteen days, depending on prevailing weather conditions and the level of plant resistance.
Sources of primary infection (primary inoculum) could be infected plants in neighboring fields, wild plants, volunteer crops or infected plants in the growers’ field, which release spores (minute balls) that reach healthy plants or healthy parts of the plant through being carried there by wind, irrigation splashes or rain water.
Spread /secondary infection
When blight spores (sporangia) land on the above ground parts of healthy potato plants, they become established and initiate primary infections under favorable environmental conditions (prolonged moist conditions) producing initial symptoms like brown blotches. When a spore lands on a healthy leaf, spore germination requires high moisture content on the leaf surface (free water) and moderate temperature.
Weather conditions that favor the spread of late blight are known as ‘blight periods’.
For the white fuzz (mycelium) to appear there must be high humidity. Most of the time mycelium appears at night because of the high humidity caused by dew. If there is rain or fog, the mycelium can appear at any time.
Favorable conditions for spread
The favorable conditions for establishment and spread of the fungal pathogen include: high humidity and warm temperatures.
The store should have shelves; and before storage the stores and shelves should be sprayed with insecticides to kill tuber moth adults. The tubers spread on shelves should be turned once a day to prevent spoilage.
The Mexican marigold or Eucalyptus leaves and branches can be placed on the tubers to repel potato tuber moth infestation.
To reduce infection, the following are recommended practices:
1. Use healthy seed potato tubers at planting.
2. Use varieties that have high levels of late blight resistance.
3. Always cover tubers with soil during hilling to prevent tuber infections.
4. Before harvesting, destroy leaves that are infected to reduce chances of tubers coming into contact with the spores.
5. Harvest tubers when they are fully mature to reduce incidences of skin damage and spores entry during harvesting and storage.
6. Chemical control with fungicide;
Apply protective fungicides (such as Mancozeb) after emergence and repeat regularly based on prevailing weather conditions. Ensure the underside of leaves is covered during fungicidal application.
For susceptible varieties start spraying protective fungicides (such as Mancozeb) when plants are 10 cm tall and repeat depending on the prevailing weather conditions
For varieties with some resistance, start spraying systemic fungicides (such as Metalaxyl) when symptoms start appearing and alternate applications of contact and systemic fungicides to avoid resistance development by the pathogen to fungicides used.
Integrated management practices
• Always plant clean or certified seeds.
• Before planting, select potato varieties that have some resistance to late blight.
• Hill or earth up exposed tubers to prevent transmission of fungus from above ground plant parts to tubers.
• Scout regularly for signs of the fungus on the underside of the leaves and stems of the plants after the plant emergence.
•Use fungicides as the last option and as per the recommended application rates by the manufacturers.
There is a need for research and inventory of many approaches to manage the condition.
2. Potato Early Blight
Early blight is caused by the fungus Alternaria solani and it is found in all potato producing regions. Despite its name the diseases are found to be more severe during the end of the growing season. The disease mainly affects older leaves. The fungus survives in soil as mycelium, on leaf debris and as spores.
Source and Spread
Sources of infection are; contaminated seed tubers and plant remnants, tools and machinery.
Spores may be spread by wind or by water droplets during rainy conditions.
Symptoms
Symptoms include dry brown spots, usually restricted by the leaf veins forming an angular shape.
Effects of Early Blight on Irish Potato
The spots enlarge and join together to form big concentric/circular rings. Affected tubers develop circular to irregular lesions, which are slightly sunken and often surrounded by raised purple to black areas.
The following measures will help prevent the occurrence of serious EB outbreaks;
Plant only disease-free, certified seed.
Follow a complete and regular foliar fungicide spray program.
Practice good killing techniques to lessen tuber infections.
Allow tubers to mature before digging, dig when vines are dry, not wet, and avoid excessive wounding of potatoes during harvesting and handling.
Plow under all plant debris and volunteer potatoes after harvest.
Avoid replanting potatoes (and tomatoes or eggplants) in the affected fields for at least 2 years if severe outbreaks have been experienced.
Although no cultivar is immune to EB, several cultivars are moderately resistant and should be planted if blight is a continuing problem.
