AGROMET INFORMATION FOR PESTS AND DISEASE CONTROL

By

Linda De Wet

INTRODUCTION

Weather is related to many pests/insects and diseases, which are bad for the development of healthy crops. We can fight to prevent the destruction of our food supply by learning more about the conditions that bring them about. If we are able to predict disease or pest outbreaks by using the weather, then we can prevent or decrease high losses to a minimum.

INTRODUCTION

DISEASES/PATHOGEN & PESTS Bacteria Fungi Virusses

HOST PLANTS

ENVIRONMENT + WEATHER

THE INFLUENCE OF ENVIRONMENT AND DISEASE ON THE HOST

BACTERIA WIND RAIN

APPLESCRABAPPLES

PEARS

SHOOTS TURN BLACK

FUNGI LOW Ta RAIN

SHADE TREESPERENNIALSTURF GRASS

LEAF SPOT DISEASE

FUNGI LOW Ta RAIN

ROOT PROBLEMS

FUNGI LOW Ta RAIN

DROUGHT-STRESSED

PLANTS

CANKER DISEASES

FUNGI

DRY CONDITIONS COLD Ta

or INTENSE

SUNLIGHT

WEATHER VARIABLES

Temperature (Ta) Relative humidity (RH) Rainfall

MODELS DEGREE DAYS / THERMAL TIME

EXAMPLES OF DISEASESCROPS

Stem and Leaf Diseases – FungalALTERNARIA BLACK SPOT, Alternaria brassicae

and A. raphani Symptoms

Black spots Survival and Spread

Soil Crop residue Seed Weed hosts RH > 80% Wind dispersal of spores

Control Crop rotation High germination (over 90%).

CROPS Stem and Leaf Diseases – Fungal

WHITE RUST, Albugo candida Symptoms

White creamy yellow pustules develop - lower leaf surface and pods

Infected flowers develop a "staghead"

Survival and Spread Crop refuse Seed Rain Cool Ta at flowering

Control Resistant varieties Three year crop rotation Control volunteer Canola and weeds

CROPS Stem and Leaf Diseases – Fungal

BLACKLEG, Leptosphaeria maculans Symptoms

White to gray spots on cotyledons and leaves Flowers blighted Few black fruiting bodies form.

Survival and Spread Seed-borne Initial spread - airborne spores Secondary spread - splash-dispersed spores Ta 21 °C Stem canker development - 24 °C day Ta Night temperatures 16 °C.

Control Plow down infected crop residue 4- year crop rotation Resistant varieties

CROPS Stem and Leaf Diseases – Fungal

DOWNY MILDEW, Peronospora parasitica Symptoms

Leaf spots initially angular, translucent, light green Stems of flower clusters become swollen Frequently associated with white rust

Survival and Spread Spores Windborne Long periods of dew, damp and cool weather and low

light intensity

Control Destroy crop refuse Crop rotation

CROPS Stem and Leaf Diseases – Fungal

YELLOW LEAF SPOT, Pyrenophora tritici-repentis

Symptoms Small yellow-brown oval spots Leaves yellow and die

Surivival and Spread Use leaf wetness meter - duration of wet leaf Rain and RH stays >90% “Smith simplified criteria”:

17h00 + rain + Ta >10 C OR rain in night + Ta >10 C at 08h00

Control Crop rotation Foliar fungicides may not be economical in many situations

SUNFLOWERS Stem and Leaf Diseases – Fungal

PHOMOPSIS STEM CANKER, Phomopsis (Diaporthe) helianthi

Symptoms Infection of lower leaves Light brown stem lesion Less chlorosis than inVerticillium

Survival and Spread Overwinters in sunflower or Crop refuse High Ta and high RH disease

Control Discing Crop rotation

ALTERNARIA LEAF AND STEM SPOT, Alternaria zinniae and Alternaria helianthi

Symptoms Circular to angular spots – leaves Dark circular spots on back of head Seedling blight

Survival and Spread Crop residue Airborne spores Wet weather + warm temperatures.

Control Crop rotation

SUNFLOWERS Stem and Leaf Diseases – Fungal

SUNFLOWERS Stem and Leaf Diseases – Fungal

SEPTORIA LEAF SPOT, Septoria helianthi Symptoms

Watersoaked spots - leaves dead areas

Survival and Spread Crop refuse Water-splashed spores Rainy weather or center pivot-irrigation

Control Crop rotation Bury crop refuse

SUNFLOWERS Head Diseases – Fungal

RHIZOPUS HEAD ROT, Rhizopus spp. Symptoms

Soft, mushy brown rot Shredding Head droops or falls off

Survival and Spread Warm moist weather Birds or hail

Control Unknown Reduce bird and insect damage to heads

SUNFLOWERS Head Diseases – Fungal

BOTRYTIS HEAD ROT, Botrytis cinerea Symptoms

Soft brown rot Wet weather - brown tissues develop velvety gray-

brown surface

Survival and Spread cool, wet conditions

Control Unknown Not severe disease

FRUITFungal infection of leaves

APPLE SCAB, Venturia inaequalis Symptoms

Apples and leaves infected

Survival and Spread Release of spores during rain Infected only if leaves stay wet Prediction uses “Mills” periods

unbroken period of 20 hours + Ta 14 C + leaves wet

Visible damage 3 weeks later

Control Resistant varieties

EXAMPLES OF PESTSTHE OLIVE FLY Bactrocera (Dacus) Oleae Symptoms

Visual inspection of fruit number of times eggs laid number of larvae number of flies hatched

Stings cause holes and a moon shaped blemish on olive

Survival and Spread Ta > 40  oC for > several hours + low RH (< 35%) inhibits Water stress impedes Lack of fruit or cold weather impedes

Control Timing of the first control measure of the year is crucial Lure and kill traps last 5 - 6 months Sprays last only days or weeks

WEATHER AND CLIMATE EFFECT ON PESTS

Weather and climate can: compete with insects and their production can be beneficial (pollinate, protect) aid as a vector (e.g. mosquito).Management of crop / stock + insect populations

NB Identify population processes How must activities of insects be managed? What is the susceptibility of hosts to insect

attack? What is the effect of global warming? This information can be utilised by decision-

makers.

1) Development Rate and Phenology Primary factor is TEMPERATURE (Ta) Degree days Warm areas - high Ta + water stress conditions Temperate areas - Ta starts slowly in spring, progresses

rapidly and slowing again in autumn Can predict phenology from climate (Ta) and to do this

one must consider: daily variations spatial differences insects with own Ta regulation

Development of mites, earwigs, moths, worms, mosquitoes, butterflies, blowflies, dung beetles, bollworms and armyworms weather parameters and weather parameters development

WEATHER AND CLIMATE EFFECT ON PESTS

2) Survival, Fitness and Population Size Mortality or death Extreme weather events Fitness of insects, means enough food which is influenced by:

indirect effect of weather and microclimate.

Use models, statistics and indexes for combination, transformation and integration of weather elements (mainly daily Ta, rain)

Optimal conditions exist for specific insects Heavy rain high mortality rates Hot, dry conditions high mortality rates Ta and rain influences ticks, aphids, grasshoppers, fruit flies, wasps and vegetable bugs

WEATHER AND CLIMATE EFFECT ON PESTS

3) Distribution of insects Insects have thresholds Tmx or Tmn + moisture stress distribution Distribution of insects - spatial over land, time or

seasons because of different spatial occupations 4) Activity Weather affects vigour in insects e.g. flight is influenced by winds Sequence of events and conditions activity Radar - locust flight patterns

WEATHER AND CLIMATE EFFECT ON PESTS

5) Migration Pests - vectors of insect-borne pathogens Locusts - Ta at dusk > 20 C + rain flight Moths – Change in season + Ta migrate Migration stops with Ta Winds migration Ta profile: with height convergence wind direction + wind speed

6) Continuity and Establishment of Infestation Crop rotation Frost - kills aphids (plant lice) Cold and drought kill insects - natural enemies Beneficial insects - bees and wasps

WEATHER AND CLIMATE EFFECT ON PESTS

7) Outbreak Initiation Rain or drought Outbreak availability of food for insects

8) Host Susceptibility Damage incurred condition of crops Crops - wind-blown, rain-drenched, water-stressed, are more vulnerable Sheep – rain and mist increase in nematodes (round-, wire-worms)

WEATHER AND CLIMATE EFFECT ON PESTS

9) Management Activities Bad weather disrupts normal management Farmers or growers - surveys + access to sprays Planting dates can be changed Efficiency of sprays depend on weather:

RH, wind, stability and rain Management - daily farm management + long term

decisions Short term decisions-use

daily weather forecaststemperaturerainfall

Long term decisions-useweather in past week / monthdeviations from normal weather patterninteractions between weather elements

GIS, satellite, models + decision support systems

WEATHER AND CLIMATE EFFECT ON PESTS

INTEGRATED PEST MANAGEMENT (IPM)

What is IPM?IPM is an approach to solving pest problems by applying our knowledge about pests to prevent them from damaging crops, harming animals, infesting buildings or otherwise interfering with our livelihood or enjoyment of life. IPM means responding to pest problems with the most effective, least-risk option

IPM applied ONLY when unacceptable levels Impact on environment must be limited Applications of pesticides - always last resort in an IPM program

IPM Soil Preparation

Suitable site Test soil Rotate crops Create raised beds Sufficient organic matter.

Planting Tolerant varieties Planting time Row spacing diseases and insects

prevention Forecasting

Pest outbreaks Treatments timed prevent crop damage +

saving sprays

Pest Trapping Traps to identify possible outbreak

Monitoring Inspection of fields to determine damaging

levels of pests Thresholds

Before treating, growers wait until pest populations reach a scientifically determined level that could cause economic damage. Before threshold is reached, cost of yield + quality loss < than cost for control

Cultural Controls Turn under crop residues Sterilize greenhouse tools Harvest early

IPM

Biological Controls Conserve the many beneficial natural

enemies

Chemical Controls Select best pesticide Calibrate sprayers Good weather conditions

Recordkeeping Pest traps, weather and treatments

IPM

Who can use IPM? Farmers Buildings and grounds maintenance personnel Professional pest control operators Home dwellers

What are pesticide risks? Humans exposed to toxic concentrations According to the WHO, > 3 million people are

severely sickened and 220,000 die from pesticides each year worldwide

In the U.S. alone, 110,000 people are poisoned by pesticides annually These are "acute" poisonings

Long-term effects include cancer, birth defects and other disorders.

IPM

Birds - 60 million to 70 million killed each year in US

Fish and other wildlife Wild bees and honey bees - essential for

pollination of many crops, but many are lost to pesticide exposure

> one-third of calls to animal poison centers pets exposed

Pests can also become resistant to pesticides control costs + crop losses + pest damage

Many natural enemies of pests killed by pesticides Pesticides are powerful medicines for pest

problems It’s not smart, effective or affordable to take

medicines when you‘re not sick Eating right and staying fit is a great, low risk

medicine for your health Using IPM to prevent pest problems is the best

solution for a healthy environment for everyone

IPM

Integrated Pest Management

CONCLUSIONS We are all aware that there is a definite increase in the appearance of

disease and the frequency with which it occurs.

Many diseases are weather-related and so we as Agrometeorologists can play an increasingly important role in the prediction of diseases.

Development of models as early warning systems can assist in prevention of unnecessary application of sprays and fungicides and so increase the profits of those involved in the production of the food resources necessary for our survival and well-being.

(soybean) RUST INVASION

http://www.youtube.com/watch?v=B32FXj4dKig