Wheat: Insect pests and their management

M. Macharia Kenya Agricultural and Livestock Research Organization, Food Crops Research Centre,

P.O. Private Bag- 20107, Njoro, Kenya.

I. Introduction

• Wheat is attacked by a number of insects, some of which inflict severe damage, while damage by others is not easily noticeable.

• Others may not cause appreciable damage on plant through direct feeding but maybe vectors of diseases, which may become a bigger problem.

Introduction …

• Insect pests damage the wheat crop either mechanically or physiologically.

• Some pests are also vectors of infectious pathogens such as barley yellow dwarf.

• For effective control, it is important that wheat growers are able to recognize the pest, damage and take appropriate control strategies.

1. Cereal aphids

• Greenbug,Schizaphis graminum

• Rose grain aphid, Metopolophium dirhodum

• Bird cherry aphid, Rhopalosiphum maidis

• Cereal leaf aphid, Rhopalosiphum padi

• English grain aphid, Sitobion avenae

• Russian wheat aphid, Diuraphis noxia

1.Cereal aphids…

• Cereal aphids are a major constraint to wheat production in Kenya.

• The aphids cause damage by directly feeding on the wheat crop.

• Also transmit Barley yellow dwarf virus (BYDV).

• 47% yield losses have been recorded on wheat.

• Outbreaks of cereal aphids and BYDV makes wheat production uneconomical, hence the need to control cereal aphids.

1.Cereal aphids…Status of Russian wheat aphid

• RWA is a recent introduction in Kenya (1995).

• Currently, the most important cereal pest.

• Losses vary from 10-100% depending on stage of infestation.

• Injects toxins causing leaf rolling.

• Feeding produces white streaks on leaves

of young plants.

• Also causes fish hooked sterile heads.

Symptoms of cereal aphids damage

Symptoms of Barley yellow Dwarf

Wheat Barley Oats

• Cultural control:

• Early planting.

• Early destruction of volunteer wheat and barley and grasses.

• Proper good fertilization to avoid stressed crops.

• Use recommended high seed rates.

Chemical control:

(i)Seed dressing insecticides

• Imidacloprid (Gaucho 350FS) @t 200ml/100kg seed.

• Thiamethoxam (Cruiser 350FS) @ 150ml/ 90kg seed.

• Clothianidin + prothioconazole (Redigo Deter 300FS) @200 ml/100 kg seed.

• Thiamethoxam + fludioxonil + difenoconozole (Celest Top 312FS) @150 ml/100 kg seed.

Management strategies of cereal aphids

Management strategies of cereal aphids…..

(ii) Foliar applied aphicides• Pirimicarb (Pirimor 50WG) @ 0.75kg /ha. • Betacyfluthrin + Chlorpyrifos (Bulldock star 262.5EC.) @

0.5l/ha. • Imidacloprid + Betacyfluthrin (Thunder OD 145) @ 0. 3l/ha• Oxydemeton- s- methyl (Metasystox 250EC) @ 0.51/ha. • Cypermethrin + Chlorpyrifos (Nurelle* D 50/500EC) @ 0.51/ha.

• Alpha-cypermethrin + Dimethoate (Alphadime) @ 0.75l/ha.

• Acetamiprid (Twiga ace 20 SL) @ 0. 25l/ha.• Cypermethrin + Chlorpyrifos (Cyclone 505 EC) @ 0.5l/ha.

2.The Red billed quelea birds

• Damage the crop after the dough stage by eating the grain directly from the spikes and causing ears to shatter.

• Damage is recognized by presence of wheat plants showing 'whiteheads' where the grain has been eaten.

•Early and late wheat crop is more liable to damage by birds.

Male in breeding plumage

Female in breeding plumage

Non-breeding plumage

Management strategies: Red billed quelea birds:

(i) Cultural control• Manual bird scaring, scarecrows and noise making devises.• Cutting trees harboring roosts and colonies.• Good weed management – (weeds attract birds).• Using reflective ribbons that scare birds from the field. • Blowing up nest colonies & roosts using fire bombs & dynamite.

(ii) Chemical controlSpraying avicides-•Fenthion 60%EC to kill the birds wherever they have roosted.

Due to its economic significance, management and control is centrally co-ordinated by Crop Protection Directorate, Ministry of Agriculture, Livestock and Fisheries.

3.Rodents

2

Multi-mammate shamba rat (Mastomys spp.)

African grass rat (Arvicanthis spp.)

• Attack at germination where rats retrieve sown seeds.

• Damage starts at early booting & continues through the mature grains.

•Damage recognized by visual observation of patches of whiteheads' in a wheat field. •Presence of completely severed stems and cut short lengths of stems on the ground between the rows.

•Presence of runways, burrows and nest sites.

Management strategies: Rodents (i) Cultural control• Disturb and destroy habitat (burrows) of the rodents.• Trapping using kill and live-traps.• Early harvesting and efficient harvesting of wheat.• Environmental manipulation, by ploughing and grazing after harvest.• Improving storage structures by rat proofing. • Minimize the alternate food sources (weeds and crop residues).

Chemical control :

Use recommended rodenticides preferably as ready-made baits :-• Bromadiolone 0.005% (Miratex, Lanrat).• Difethialone 0.025% [Baraki]• Flocoumafen 0.005% [Storm)• Zinc phosphide 2.0% . 

Poor post harvest management can lead to:-

• Rapid deterioration in grain quality

• Decreasing germinability

• Decreasing nutritional value

• Development of grain storage pests and mould development ( mycotoxins).

4.Major Insect Pests Of Stored Wheat

Major Pests Of Stored Wheat

i

Weevil Larger grain borerLesser grain borer

Indian meal mothAngoumois grain moth Rats

Management strategies: Stored insect pests

To reduce the potential of infestation

• (i) Grain must have grain moisture content not higher than

9-12%.

• (ii) Store should be cleaned and treated with (Pirimiphos –

methyl spray –(Actellic 25EC).

• (iii) Regular monitoring of the store and grains.

Chemical control. Always use approved insecticides.

• Malathion + permethrin (Skana Super).

• Pirimiphos-methyl + permethrin (Actellic super) .

• Pirimiphos –methyl +Thiamethoxam (Actellic Gold).

These are applied at 50g / 90 kg of wheat grains.

Conclusion

• Frequent scouting and monitoring of the crop under field and grain storage conditions to identify possible pest problems is important.

• Wheat must be harvested in a timely manner before shattering, pre-harvest sprouting damage, bird damage and weathering.

• Educating and training farmers on pre & post harvest operations would greatly help in reducing yield losses in wheat.

Thanks