Posts Tagged ‘chinch bugs’

Field Notes, July 2, 2010, Chinch bugs, Gramoxone injury, Straighthead disease

July 8, 2010

chinch bug injury to rice paniclesLast week I mentioned chinch bug injury to seedling rice.  Normally if chinch bugs are a problem they affect seedling rice that is not flooded.  By this time of year we do not expect to have chinch bug problems.  In this case panicles were injured by overwhelming numbers of chinch bugs in the panicles.

Adult chinch bugs appear to have a white spot on their back which is actually the tips of its wings that are folded over its back.  Chinch bugs have piearcing -sucking mouthparts.  They literally suck the juices out of the plant.  If only a few insects were present injury would likely not be noticed.  In this case the panicles were loaded up with chinch bugs.

Immature chinch bugs are bright red and wingless.  They feed the same way the adults do, by sucking sap out of the cells.  As they grow they become darker.  Most of the time we ingnore them when they are found at this stage of growth, but in this case the injury was significant and the field was to be sprayed to control rice stink bugs anyway so an insecticide that would control both was applied.

Gramoxone injury looks much worse than its effect on rice when it drifts on to rice.  While the spotting causes the field to look burnt and heavily spots the leaves, it is a situation where “what you see is what you get.”  When new leaves emerge they will be fine.  Heavy spotting of flag leaves could cause a problem, but it would have to  be severe.

Straighthead Disease in Rice

 

Straighthead disease of rice gets its name from the failure of grains to fill and the consequent upright appearance of the panicles.  Because there is no grain development the panicles do not nod over; they remain straight.  It is a physiological disorder, not a disease caused by a plant pathogen.

"Parrot beaking" of spikelets

One of the more obvious symptoms of straighthead is the distorted spikelets commonly called “parrott beaking”.  Similar symptoms can be observed when glyphosate drifts on to rice past internode elongation.  Many times there is no indication of drift until the heads emerge.  Some varieties are more prone to straighthead than others.  If straighthead has occurred in a field it is likely to occur again so a resistant variety should be selected.

Normal Flag Leaves on Straighthead Affected Plant

 

One way to separate straighthead from glyphosate injury is to examine the flag leaves.  If the problem is straighthead the flag leaves are normal in size and configuration.  In the case of glyphosate injury the flag leaves will be greatly shortened and are often twisted as well.  Panicles are also shortened when affected by glyphosate but are of normal length if the problem is straighthead.

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Field Notes, June 28, 2010, Cercospora, chinch bugs

July 8, 2010

We used to call this disease Narrow Brown Leaf Spot, but because of its confusion with Brown Spot and the devastating impact it had several years ago we now refer to it as Cercospora.  Cercospora is the genus name of the fungus that causes the disease.  These symptoms tell us infection has already occurred, but is not the yield limiting phase of the disease.

This is  a close-up of some of the same leaves shown in the first photograph.  One major characteristic of this disease is the linear brown spots on the leaves.  They follow the veins of the leaves.  The phase that causes the most yield damage is the net blotch phase that shows up on the sheath of the flag leaf and on the stem.

Most of the time chinch bugs are a pest when they feed on young seedlings in rice fields that are not flooded.  Once the fields are flooded we usually forget about chinch bug injury to rice.  In this case seedling rice was being flooded late in the year and chinch bugs were reducing stand.  We expect the flood to take care of the problem.