Posts Tagged ‘spider mites’

Field Notes June 21, 2010; Colaspis, crazy rice, guttation, spider mites

June 23, 2010

This is the adult of the Colaspis beetle whose grub feeds on the roots of rice.  It was called the Grape Colaspis until entomologists determined it is not that species.

Until the actual identity of this rice plant can be determined I am calling it “crazy rice”.  It is much taller than the CL151 in which it was found, it is glabrous (smooth), and the lemma (the big half of the hull) is awned.  It does not fit any of the descriptions of wild rice I have studied.

As mentioned in an earlier post, this is the first time I have seen spider mites in rice.  In this image several are visible.  I think if you click on the image you can enlarge it.  Stuart Gauthier, county agent in Vermilion parish found them in one field along an edge.  Initially I lost the actual sample, but we returned to the field and confirmed them.

This year a lot of fields were flooded later than is recommended.  In this case it also meant nitrogen fertilzer was applied later than recommended.  The combination of establishing permanent flood late and delaying nitrogen application caused the yellowing of the lower leaves visible in this field.  The plants are also shorter than they should be at this stage of development.

Water of guttaton always makes a good photograph.  It is caused by the buildup of water pressure in the plant beginning late in the evening and continuing until early morning.  After daylight photosynthesis begins, the stomates open and a water deficit begins to occur in the plant.  At that time the droplets may actually be drawn back into the plant through the pores called hydathodes at the margins of the leaf.  More often they just evaporate or fall off the plant.

Field Notes June 14, 2010; black rice bugs, spider mites

June 14, 2010

Symptoms of spider might injury to rice leaves

The narrow white spots on the leaves of this rice plant are mostly a result of spider mites feeding on the leaves.  Some of the white scars are the result of rice water weevil feeding.  In general the spider mites cause more frequent lesions and they are a little more rounded at the ends than those caused by the rice water weevil.

Spider mite feeding signs on rice leaves

A closer view of the feeding signs of spider mites on rice leaves reveals more detail.  Most of them are more rounded at the tips than those of the rice water weevil.  In some cases the areas are only faintly white.  The rice water weevil feeds by actually chewing away the leaf cells leaving the lower epidermis and cuticle intact creating a sort of “window pane” effect.  Spider mites essentially suck the juice out of the cells causing dehydration.

The yellowish object in top center of the photo is a spider mite

 

In this image a single spider mite can be seen on a rice leaf.  They are larger than the panicle rice mite.  While they have been reported in greenhouses before this is my first time to see them on plants collected in the field.

Greatly magnified image of a mature and an immature spider mite

 

The image at right is a greatly magnified image of two of the spider mites found on rice leaves.  The mite on the left is an adult and the one on the right is immature.

Louisiana black rice bug injury symptoms

 

Each year for the past several we have seen an increase in the incidence of this type of injury.  It resembles stalk borer damage, but is not from a borer.  It is infrequent, but fairly common.

"Louisiana" black rice bug adult

 

We originally called this insect the black rice bug until we were told that common name was already assigned to another species.  Until we have an official common name we are referring to it as the “Louisiana” black rice bug.  When it feeds it causing firing of leaves often more on one side of the mid vein of the leaf than the other.

Beetle and feeding signs on rice leaf

 

Dr. Natalie Hummel found this beetle (yet to be identified) feeding on rice leaves in Madison parish.  It causes symptoms that resemble those left by feeding of rice water weevils.  She noticed lots of feeding signs without the presence of heavy populations of rice water weevil that would have been expected.

Beetle feeding on rice leaf

 

This is a close up of the beetle Dr. Hummel found feeding on rice leaves.  When she has a positive ID of it I will update the blog.