Rodent Tales

Environmental News Issue 28 Winter 2011

Gerald and Kaity Endt of Okiwi Passion are relentless in their pursuit of the midnight melon marrauders – their passion for production of excellent organic food has made them popular with both humans and rodents. This is their story.

Subject: Mr Rat (definitely male, because I found him)

Size: Massive, extremely well-fed

Type: Ship Rat var. slicer (refers to the sign he leaves behind)

Number of lives: 3 that I know of

Diet: Butternut and delicata squash seeds, probably macadamias before that.

At Okiwi Passion over the summer harvesting period we have a huge explosion of rats in a very small area (only about 2 acres are in vegetable production). We are surrounded by waterways, have bamboo shelterbelts and groves of bananas so they love us! Their attacks on our crops are relentless throughout summer and autumn and one cannot for one moment have the remotest thought that ‘we now have everything under control’, because the minute the trap lines are resting, it’s like you have never trapped.

The crops they have wreaked havoc with include melons (but not water melon, shhhh!), pumpkin, capsicum, especially when they are red, kumara, tomato, corn, with lesser test bite damage to zucchini and eggplants. We have even found strawberries carried off several metres to a stash under some zucchini leaves.

Rats (and mice) are generally after seeds which are so high in energy and protein. Once an entire crop of capsicums was raided over a week’s period, leaving the gutted fruit dangling on the plant, still edible but unsaleable of course. Hundreds of dollars’ worth of sales lost. Melons get attacked as soon as they ripen and develop that delicious aroma. Again most of the flesh is untouched, just a large hole through to the seed cavity and a messy pile of seed husks by the melon. Interestingly they have not yet attacked the watermelons which are completely unscented. The number of pumpkins of all types that we have lost over the past three summers would feed a small army.

Corn is a very hard crop to protect once the rats discover the kernels. The peanut butter finds it hard to compete. We have had traps around the perimeter of the corn block before the kernels mature, with a minimal catch rate. Once the corn has fattened up and been discovered, the increase in numbers caught is phenomenal.

As for kumara, it is a sad sight to be digging up a huge kumara that would easily have weighed 1.5 kg only to find it has been pretty much hollowed out. A kumara row must be rat heaven – safely hidden in the soil and the kumara vines, they tunnel their way through a veritable feast of high carb food. Oh, did I mention the seeds neatly and methodically taken from seed trays in the green-house? Once even the lettuce seeds were stolen – hardly a mark made in the potting mix, it must have been a wee mouse. Gerald has had to make some great rat excluding cages for our seed trays, can’t do without them in spring when the rats are hungry!

From that second summer of losing the bulk of our capsicum crop and half the kumara, we have learned a lot and developed a few strategies.

Over winter and spring the traps get set around the perimeter of the cropping blocks as the rats are out in the bamboo and surrounds, moving the traps every 6 days or so, then we focus on the summer crop zones as they mature. At this stage it is really important to notice the first signs of rat damage, as the word seems to get around so fast.

We use a combination of cage traps and Protecta snap traps in the black plastic box. For bait we use peanut butter sometimes embellished with macadamia nut pieces, saved and dried pumpkin seeds, corn kernels stored in the freezer etc. Rats are very clever creatures and if one escapes from a particular setup it will never go back there, so you have to change things all the time. Our 40 odd traps get set and rebaited if necessary each late afternoon and checked the next morning, when we also close all the cage traps as the banded rail seems to have a bit of a taste for peanut butter too.

We only use poison as a very last resort – when a Mr Rat refuses to be caught and inflicts continuous damage. Then we use the multi-feed poison blocks set on a wire stake set among the target crop with no enclosure as by now Mr Rat will be trap shy. The bait gets set each late afternoon and removed at dawn so birds don’t eat it.

An example of having to do this took place in the pumpkin block in the summer before last. Our dog knocked a cage trap out of our Japanese woofer Kasunari’s grip, the door opened and out sprang the rat. We also found a box trap that had gone off, but no rat, only some fur. We then had a situation over 2–3 weeks where many traps were set in the butternut row in a specific area and no rats caught, but a whole lot of damage. I started to introduce multifeed poison inside stations but after a week, zero take. At this stage I was starting to get visions of Houdini, giant, cunning, so he was called Mr Rat, named after others who have had similar escapes. As a last resort we laid poison loosely right next to the butternut for five nights. On each night I got results. On day five I was mowing the grass around the bananas, where the chooks were kept at the time, and adjacent to the pumpkin block, when I noticed a group of chooks staring at a particular spot. There I saw a spaced out, groggy, gisnorcorus rat sitting just outside his hole. He was immediately terminated, and I had good reason to parade him around the property. From that day, there was no further damage to the crop.

This year we had to use the poison for the melons over a one week period, again after endless onslaughts on the crop. We used looped wire with the poison on with no cover, and laid them every night from dawn to dusk. This proved very effective.

Last year was our best control (except for Mr Rat’s endeavours ), with about 10% damage to targeted crops. I guess like everyone else it’s a lot trial and error.

We would really like to thank Judy Gilbert for her time as we have consulted with her over rat trapping strategies, and for loaning us various rat traps to experiment with. We are looking forward to trying out the new wooden ones. Tonight they are set among the late autumn capsicums…