Week 4 - Estimation of crop damages

Part I.

In the soybean leaf samples

1. T he damage caused was most likely due to insects with chewing type mouthparts. This is the only explanation for the missing portions of the leaf centers and edges. In the week 3 blog where we had to identify insects that were collected within a soybean leaf sample from Scandia, Ks, the majority of the insects that were found exhibited chewing type mouthparts. Some of the different orders were either Orthoptera adults or Lepidoptera larvae. In this portion of the activity, all of the damage looked as though insects had caused it at some point, so therefore it is indirect circumstantial injury to the soybean leaves. I would describe this damage as

2. The sampling unit in this case was a single plant leaf from a soybean plant (may have been many whole plants involved). The sampling size that was used in this lab for the soybean leaves was 50 leaves. I would say that in a scouting situation a collection of at least 5-10 plants from an affected area, if it was a field wide issue, then more samples may be necessary. From these plants then you would need to analyze the plants based upon the parts that were injured (in this case, the leaves). The method that I utilized to quantify the damage was by calculating the percentage of leaf loss based on the total estimated leaf area. From this I would then try and quickly gauge what the rest of the leaves seemed like in comparison for the rest of the set.

In the Corn ears and Sunflower heads

1. The corn ear showed external chewing on some kernels and also some boring of insects into the kernels. The corn damage was probably caused mainly by larval Lepidoptera that would eat into the ear before the corn was fully matured and dried. The sunflower heads had what looked like the tops of the seeds had been sliced off or dug out, this could be caused by chewing insects (or a knife). This type of damage would probably be done by some Lepidoptera larvae or possibly an Orthoptera adult also, the fully removed seeds would probably be caused by birds. Typically in sunflowers the damage that occurs from insect larvae is actually inside the stem or head where they are safe to feed without the risk of predation.

2. The sampling units in the corn case were corn ears and in the sunflowers it was a fully mature sunflower head. The sampling size was 30 ears of corn and 10 sunflower heads. For the corn it was quite a bit more difficult to estimate the damage since it was not just laying out flat. In order to estimate the damages I tried to roughly calculate any damages that I saw into a total percentage of damage, I was not very successful at this. In the sunflower heads it wasn’t too hard to gauge the grain damages since it was layed out in a flat surface. To estimate the damage I also tried to gauge the damaged portions versus the unaffected portions, I was fairly accurate but not perfect by any means.

3. This method would be a relative measure of the amount of leaf tissue that was missing; it would be very difficult to do an absolute measurement in one field, let alone multiple fields. The measure of the leaf loss would be categorized as absolute if the leaves were analyzed more accurately with measurements of the total leaf area vs the missing parts. A faster method of accurate measurement would require scanning the leaves into a file on the computer and calculating the missing material with a specialized computer program that can make the calculations of the leaf losses.

Part II.

4. In this experience with the accuracy of damage prediction in 3 crops, I would say that as more samples were added to the sample unit that my accuracy dropped. In the soybean example there were 50 samples to look at which made consistency key to keep the accuracy high. The corn and sunflowers had much fewer samples so it would be expected for this damage analysis to be more accurate.

5. In comparison with the rest of the class I did worse than I would have hoped, as notated by the next three graphs.

For the soybeans I was accurate to a level of 1.49 and precise to an R² of 0.88, since this was a fairly large sample size I was fairly pleased with this result. The best score was from Michael Davidson: slope of 1.27 R2 of 0.93, he overestimated on average but was still in the 93% accurate range. Since I was somewhat higher on the overestimation, I could have become more accurate with a lower level of estimation.

The corn samples were from a smaller sample size but due to the type of sample (corn on cob) it was more difficult overall for the class to properly judge what percentage of damage was incurred. I achieved 0.34 accuracy and an R2 of 0.19. This was not very good but it was not the worst in the class. The best judge for the corn damages was Tanner Robbins: slope of 1.07 R2 of damage 0.69.

For the sunflower example, we had the lowest sample size of only 10. I was very accurate on this sample at 1.00 and a 93% precision rate. The best analysis in the class came from Kim Kerschen: slope 1.17 and R2 of 0.99, a lot of the class was able to do well on this crop and I attribute this to the smaller sample size.

If we were to conduct another exercise like this I would definitely ask the top damage estimators from the class what their methods were so that I could improve upon my ability to estimate crop damages.

6. This exercise was useful in the sense that it can show someone how easy it is to over or underestimate crop damages in the field. In the event that it was necessary to make a quick decision on whether or not to utilize a control method upon a pest, precision would be a must in order to properly advise a producer. Higher accuracy when analyzing how much damage has been caused is an integral part of making a precise reading.

week 3 lab 'what's in the bag?'

For this lab my partner and I worked to identify and categorize the insects that we found in a sample from two crops, alfalfa and soybeans. Both crops contained a multitude of insect diversity, but there were alot more present in the alfalfa sample.

This sample contained 6 seperate orders of insects and about 11 seperate species. We categorized them by their types of mouthparts and there were 3 types, piercing/sucking, rasping, and chewing. Not all of the insects were at the same stages in their lives and there were also some variations in sizes. For my closeup I used a stinkbug, order Hemiptera, to show the parts of a piercing sucking insect. With this type of eating habit, the stinkbug will pull it's mouthparts flat with it's abdomen, when this insect is standing prone, the mouthparts are not very visible. When feeding it will point the mouth parts down to poke into leaves and stems to pull the juices out.

In the soybean sample there were only about 5 different species of in the collection and my partner and I labeled them into 3 different orders. Each of the specimens exhibited chewing type mouthparts. I have labeled a grasshopper that was found in the sample (not the exact grasshopper in the blown up picture). Since the grasshopper has chewing mouthparts it's head is more pronounced than the stinkbug and more of the mouthparts and 'face' are visible when it is prone on the ground.

IPD Who dun it?

On the late planted grain sorghum we found that there were many different feeding patterns shown on the leaves.

The first was a random slothole pattern which probably occurred before the leaves had fully unfurled and other edge feeding, the edge feeding could be explained as late feeding by something like a caterpillar or grasshoppers and then wind damage that may have happened after the fact. Very few live insects were found on this sample.

Along the stem next to the leave sheath, there was some frass left over from fly larvae that was observed feeding when we dissected the plant.

Some windowpaning was seen at some places along outside leaves. Which would have been caused by another insect with smaller chewing mouthparts.

With the late planted soybean samples there was windowpaning observed on some of the leaves. A caterpillar was observed on the plant.

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There was also a possible disease present that was causing leaf chlorosis to appear.

The early planted sorghum showed that there was some circumstantial head feeding occurring, it was difficult to see without peeling back the panicles of the seedhead. It was evident that yield loss had already taken place.

There was also some insignificant mucous observed around a leaf collar.

In the sunflower plant it was evident that there was circumstantial feeding that had taken place on the leaves.

There was no damage seen to the head of our plant but it was stunted and this could be attributed to compacted soil, since the roots looked like they were not allowed to grow very deep.

The plant that we cut open showed now damage to the stem but in another group there was a stem boring caterpillar that had caused some damage.

The corn plant showed circumstantial evidence of an ear borer worm, and some ear mold.

There was also a caterpillar observed as direct evidence of some leaf feeding.