Watch out for those aphids!

Farmer's Weekly (South Africa) - - Contents - FW

As a vi­ral in­fec­tion in your cu­cur­bit crop is such a big prob­lem, not to men­tion al­most in­evitable, it’s worth ex­pand­ing on what I wrote last week.

Usu­ally, on the Highveld, viruses be­come more com­mon in the New Year, but start much ear­lier on the Mid­dleveld.

Baby mar­rows are par­tic­u­larly vul­ner­a­ble as they are nor­mally picked ev­ery other day. This amount of han­dling can cause a virus to spread very rapidly. It is trans­mit­ted through the sap.

An ef­fec­tive pre­cau­tion is to break the fruit off the plant and trim it in the pack­house. This may seem like ex­tra work, but cut­ting the fruit off the plant in the land with a knife will in­crease the speed of in­fec­tion.


Baby mar­row farm­ers usu­ally em­ploy suc­ces­sive plant­ings for har­vest con­ti­nu­ity over a long pe­riod. In do­ing so, it is only nat­u­ral to have suc­ces­sive plant­ings next to one an­other for eas­ier spray­ing and other tasks. But again, this makes it far eas­ier for the virus to spread.

Where fea­si­ble, space sub­se­quent plant­ings as far as pos­si­ble from one an­other.

Bear­ing in mind that aphids are the main vec­tor of viruses, carry out the first plant­ing on the lee­ward side of the farm (that is, down­wind of the pre­vail­ing winds). The se­cond plant­ing should then be on the wind­ward side (up­wind of the pre­vail­ing winds). The winged aphids will then be less likely to be blown into the se­cond plant­ing.

With suc­ces­sive plant­ings, you are also likely to be har­vest­ing from the first batch as the se­cond starts to come into pro­duc­tion. And you need to be very care­ful here.

Avoid har­vest­ing the old plant­ing and then mov­ing the work­ers straight into the new plant­ing. This will in­crease the chance of in­tro­duc­ing a virus into the se­cond plant­ing.

Be­cause a virus in­fes­ta­tion is in­evitable at some point, es­pe­cially when grow­ing mar­rows or patty pans, many farm­ers plant early va­ri­eties in order to har­vest as many fruit as pos­si­ble be­fore the on­set of a virus.

Some farm­ers even get the pick­ers to rinse their hands in dis­in­fec­tant fre­quently dur­ing har­vest­ing to fur­ther re­duce the chance of a virus spread­ing. (Milk can also be used as a dis­in­fec­tant.)


Al­though virus-re­sis­tant va­ri­eties are avail­able, re­mem­ber that re­sis­tance is not im­mu­nity; it merely re­duces the sever­ity of symp­toms. There­fore don’t be lulled into a false sense of se­cu­rity when plant­ing a virus­re­sis­tant va­ri­ety. You should still take ev­ery pre­cau­tion pos­si­ble to pre­vent and re­duce the spread of viruses.

Don’t wait un­til you spot aphid dam­age; in­spect the crop fre­quently, pay­ing par­tic­u­lar at­ten­tion to the un­der­side of leaves and de­vel­op­ing buds. Re­move dam­aged plants im­me­di­ately.

Aphids be­come in­fec­tious im­me­di­ately af­ter prob­ing an in­fected plant, but won’t re­main so for long, un­less they feed for a day or more.


I can­not over­state the im­por­tance of scout­ing your crop reg­u­larly, es­pe­cially early in the sea­son, when plants are in dan­ger from aphids that have fed on in­fected weeds.

In short, cu­cur­bit grow­ers need to be­come very aphid-con­scious! • Bill Kerr is a veg­etable spe­cial­ist and a breeder of a range of veg­eta­bles. Email him at farm­er­[email protected] cax­ Sub­ject line: Veg­etable pro­duc­tion.


ABOVE:Aphids be­come in­fec­tious im­me­di­ately af­ter prob­ing an in­fected plant, but do not re­main so for long, un­less they feed for a day or more.


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