Common Vegetable Diseases. Claudia Nischwitz Extension Plant Pathologist Utah State University

Transcription

1 Common Vegetable Diseases Claudia Nischwitz Extension Plant Pathologist Utah State University

2 Tomato, pepper and potato diseases

3 Alfalfa mosaic virus Alfalfa mosaic virus (AMV) is a virus usually found on alfalfa where it does not cause many problems Aphids transmit AMV from alfalfa to nearby vegetables Aphids acquire the virus by feeding on infected plant and deposit it when feeding on a healthy plant

4 Alfalfa mosaic virus - tomato

5 Alfalfa mosaic virus - pepper Peppers from infected plants taste bitter

6 Alfalfa mosaic virus - basil

7 Beet curly top virus Transmitted by beet leaf hopper Symptoms: Yellowing leaves, often purple veins Leaves are cupped Plants are stunted Management: Cover plants for the first 6-8 weeks after transplanting with a fine mesh Plant border rows with non-susceptible crops that shield tomatoes

8 Beet curly top virus - tomato

9 Tomato spotted wilt virus Tomato spotted wilt virus (TSWV) is an important pathogens of tomato, pepper, tobacco and peanut in the U.S. Thrips have to acquire the virus as larvae to be able to transmit it as adults. Once larvae are infected, thrips carry and transmit the virus throughout their entire lifespan.

10 Tomato spotted wilt virus TSWV is not seedborne Plants get infected early in the season Symptoms: Necrotic spots on leaves Stunting of plants Necrotic rings on immature fruit Chlorotic ringspot on mature fruit

11 Tomato spotted wilt virus

12 Tomato spotted wilt virus - peppers

13 Tomato spotted wilt virus Management: Resistant varieties Reflective mulch Insecticides (potential resistance problems)

14 Tobacco/Tomato mosaic virus Not spread by insects Seedborne Spread by humans on hands, pruning tools, clothes Survives in cigarettes Can survive in plant debris and trellises

15 Tobacco/Tomato mosaic virus

16 Tobacco/Tomato mosaic virus - Pepper

17 Tobacco/Tomato mosaic virus Management Certified virus-free seed Wear gloves when planting (smokers) or when dealing with infected plants Wash trellises with strong soap or detergent solution or 10% bleach solution Wash hands Wash clothes with hot water Remove plant debris

18 Pepper mottle virus Transmitted by aphids Can survive in nightshade weeds, volunteer peppers, tomatillos and Datura Symptoms: Mottling and mosaic on leaves Misshapen fruit

19 Pepper mottle virus

20 Pepper mottle virus Management Good weed and volunteer plant control Clean transplants Good insect control only helps if aphids are prevented form entering the field

21 Early blight Causal agent: Alternaria solani Infects leaves, stems and fruit Symptoms: Irregular necrotic spots on leaves often surrounded by a halo Severely infected leaves fall off Stem lesions are sunken and lens shaped Large lesions on leaves and stems show concentric rings Fruit infections occur through the calyx; may have concentric rings Fruit drops prematurely

22 Early blight Stems of infected seedlings or transplants are girdled collar rot For infection, warm (75-84F) and humid conditions needed Free water on leaves, can result in spore germination in less than one hour at temperatures above 80F Infections often on older tissue From infection to symptoms 5-7 days Spores are spread by wind and splashing water Other hosts: Pepper, eggplant, potato and some weeds

23 Early blight Courtesy W.R. Stevenson Courtesy W.R. Stevenson Courtesy W.R. Stevenson

24 Early blight

25 Early blight Management: Use pathogen-free seed Remove infected plant material (vines, leaves, fruit) from the field Remove volunteer tomatoes, weeds in nightshade family prior to planting Avoid overhead irrigation or time irrigation to result in short leaf wetness Plant spacing for good airflow Some tomato cultivars have some level of resistance

26 Early blight Management: Chemical control: Chlorothalonil (application every 7-10 days) Azoxystrobin (Quadris) Boscalid (Endura)

27 Late blight Causal agent: Phytophthora infestans Infects leaves, stems and fruit Symptoms: Irregular necrotic spots on leaves Infected leaves fall off and defoliation can occur rapidly Brown lesions on stem Firm brown spots develop on fruit

28 Late blight Under high humidity white mycelium can be seen on necrotic lesions After infection, lesions develop within 3-4 days Each lesion can produce 100, ,000 sporangia per day; each sporangium can cause new infection Disease and sporulation occurs mainly between 60-70F and leaf wetness of hours

29 Late blight - tomato

30 Late blight - potato agsci.oregonstate.edu nysipm.cornell.edu

31 Late blight Management: Remove infected plant material (vines, leaves, fruit) from the field/yard Remove potato culls Remove volunteer tomatoes, weeds in nightshade family prior to planting Use disease-free transplants Plant spacing for good airflow Some tomato cultivars have resistance Mountain Magic, Plum Regal, Legend Red Pearl

32 Late blight Management: Chemical control: Chlorothalonil Azoxystrobin (Quadris) Copper

33 Bacterial speck on tomato Caused by Pseudomonas syringae Bacteria survive in soil, plant debris and seed Dispersed by rain and irrigation Management: Use disease-free transplants Avoid overhead irrigation Copper spray in early planting Crop rotation

34 Bacterial speck on tomato

35 Potato -? Two possibilities: 1.Zebra chip disease 2.Physiological condition

36 Physiological condition - Causes Brown center cool soil/air temperature during tuber initiation excessive soil water, or excessive fertility (N) Internal brown spot temperatures are very high conditions are dry, and soil moisture levels fluctuate Black Spot/Black Heart low oxygen levels in tubers Too high or too low temperatures in storage

37 Zebra chip disease - potato Causal agent: Candidatus Liberibacter solanacearum Infects leaves and tubers Transmitted by psyllids It can infect tomatoes and peppers Symptoms: Upward rolling and cupping of leaves Yellowing and/or purple discoloration of leaves Sunken stolons Brown stripes in potato tubers

38 Zebra chip disease - potato hortipm.tamu.edu

39 Tomato and pepper Symptoms on tomato can look very similar to curly top virus Symptoms on pepper include misshapen leaves, leaves are light green, stalks are short and flowers may drop

40 Zebra chip disease - potato Management: No resistant cultivar available Sticky cards can be used to detect adult psyllids Control psyllids with insecticides starting atplanting (for example: imidacloprid) and continuing throughout growing season with other insecticides such as abamectin, spirotetramate etc (Contact Diane Alston at USU for more information on insecticides)

41 Onion diseases

42 Iris yellow spot virus - onion Iris yellow spot virus (IYSV) is transmitted by onion thrips

43 Symptoms: Iris yellow spot virus Diamond-shaped necrotic lesions Leaves will turn necrotic

44 Iris yellow spot virus - onion Management: No resistant cultivar available Treatment with insecticides for onion thrips Good weed control Remove volunteer onions Destroy cull onions

45 Post-harvest storage disease - onion Causal agent: Botrytis aclada Infects bulbs Can be seedborne but also present in soil, spores are airborne 100% loss in storage possible Infection occurs through the neck Infected bulbs are symptomless until 1-2 months in storage Symptoms: Onions start to rot from the neck down

46 Post-harvest storage disease - Botrytis neck rot onion

47 Post-harvest storage disease - onion Management: Infections often occur when necks are still green and succulent at harvest and spores land on it Healthy onions with well-cured necks seldom show neck rot in storage Storage conditions should be F and 70-75% humidity Seed treatment with Thiram

48 Pumpkin, gourd, melon and other cucurbit diseases

49 Watermelon mosaic virus Transmitted by aphids Survive in alfalfa and weeds Symptoms: Mosaic and distortion of leaves Bumpy fruit Color breaking of fruit Reduced yield

50 Watermelon mosaic virus

51 Watermelon mosaic virus

52 Watermelon mosaic virus Management Resistant varieties Resistant zucchini, pumpkin varieties available No resistant winter squash varieties Aphid control before they move to vegetables Use non-susceptible plants or resistant varieties as borders

53 Rhizopus storage rot Fungus is present in soil Enters fruit through wounds created by insects, blowing sand or equipment Management: Reduce injury to plants

54 Powdery mildew Obligate parasite needs living tissue to survive Damage in vegetables is mainly caused by the reduced ability of the plant to photosynthesize due to the leaves being covered with fungal mycelium It doesn t kill the plants Erysiphe cichoracearum and Podospahera xanthii In Utah: P. xanthii (Race 3)

55 Powdery mildew In some cases when leaves get necrotic and fall off fruits can become sunburned Does not need free water on leaves to infect; Rain can actually have a negative effect on the fungus Spread of PM: Conidia can be carried for miles by wind Infected plants contacting non-infected plants Dispersal by humans

56 Cultural Management Resistant varieties if available (no resistant varieties for Race 3) Remove infected plant material at the end of the growing season to prevent overwintering Plant spacing Chemical control Sulfur products work well for most powdery mildews; Do NOT apply sulfur above 90 F plants can get burned Kaligreen (potassium bicarbonate) Chlorothalonil (active ingredient)

57

58 Management On ornamental often not necessary Cultural Resistant varieties if available Remove infected plant material at the end of the growing season to prevent overwintering Plant spacing Chemical control Sulfur products work well for most powdery mildews; Read the label if the product is registered for the crop Do NOT apply sulfur above 90 F plants can get burned Kaligreen (potassium bicarbonate) Chlorothalonil (active ingredient)

59 General vegetable problems

60 Root-knot nematodes Microscopic roundworms New introductions to fields occur by Using contaminated equipment Planting infected transplants or seed Resistant varieties Disinfect and clean equipment

61 Nematodes - Management Resistant varieties Disinfect and clean equipment Crop rotation (alfalfa stem nematode) It will reduce the number of nematodes in the soil, not get rid of them

62 Nematodes

63 Root-knot nematodes