Australian Truffle Pest & Disease Newsletter

2018 Harvest damage assessment

We’ve been working with a number of truffle orchardists over the last two seasons to assess the level of damage at harvest. The data is being examined to determine the relationship between depth at which truffle grow and damage, confirm the relationship between the level of damage seen at harvest and the number of pests, particularly slaters and slugs, from monitoring earlier in the season and estimate the economic cost of invertebrate damage as well as rot.

This year we visited six orchards three times each over the course of the harvest season. There were also some other orchards visited on one-off occasions.

Each time we visited, we collected 50 random truffles, which were sorted into:

  • Exposed - breaching the surface,
  • Shallow - top of truffle within 25mm of soil surface and
  • Deep - top of truffle more than 25mm below the soil surface.

These truffles were washed and assessed for damage, then trimmed and graded by industry professionals to the industry standards. When assessing damage, where possible we attributed it to a particular pest or groups of pests. This is not always easy to do as many pests are no longer present in the truffles by the time they are harvested and the damage they cause is the same or similar. If you’d like to know more about assessing harvested truffles see out page on Assessing invertebrate damage to truffles at harvest and grading.

What we found

We saw the trend of more damage in exposed truffles as was the case last season. The chart below combines data from all orchards visited. It has the percentage of truffles with damage on the vertical axis for the three different depths.  The red section of each bar is the percentage of damage attributed to slugs and slaters. The brown section is damage attributed to rot and all other invertebrates. As you can see across all orchards that we assessed this harvest slugs and slaters were responsible for almost two thirds of the damage in exposed truffles and over half of the damage in deeper truffles.

chart
Slugs and slaters were the major group causing damage to truffles.

When you look at rot alone there is the same trend of less damage with depth, as seen in the chart below. This data includes fully rotten truffles found during harvest as well as those with patches of rot that could be trimmed out.

chart
On average across orchards the percentage of truffles with rot declined with depth in the soil at which it grew.

The graphs above were averages of all properties. The following two graphs breakdown the results for the individual orchards that we visited at least three times this season. The properties are labelled A through to G; exposed truffles are the green bars, shallow are orange, grey are deep and blue is the average of all depths.

The next chart show the percentage of truffles with damage attributed to slugs and slaters. In almost all cases the exposed truffles had the highest percentage of damaged truffles.  Very few slugs and slaters were found on properties A and E as part of our monitoring and they also had low levels of damage attributed to these pests. Property G had one of the highest slater numbers of monitored orchards.  As you can see 100% of the exposed truffles in property G had some level of slug and slater damage.

chart
The level of slug and slater damage varied greatly between orchards. Orchard A experienced less than 5% of truffles with damage over all depths and orchard G had 100% of exposed truffles with slug and slater damage. The final four columns are the average for all monitored orchards at the different depths.

The next chart shows the same properties, this time with the average level of loss per truffle due to slug and slater damage. Again, the exposed truffles are hardest hit. Looking closer at property G not only did 100% of exposed truffle have some sort of slug or slater damage but on average 30% of each exposed truffle was eaten.

chart
Across all orchards exposed truffles had the highest levels of damage attributed to slugs and slaters compared to truffles from greater depth.

There is a large amount of variability across orchards in the amount of damage seen at harvest. But if we just look at the average across all orchards (the last grouping of columns on the chart above) the high level of damage in the exposed truffles compared to deeper ones is very obvious. This shows that on average 6% of every single exposed truffle we harvested this season had been eaten by slugs or slaters.

We don’t think slugs and slaters actively seek out truffles. They are wandering the orchard floor and if they come across something tasty they stop and eat. They are much more likely to come across an exposed truffle, or a shallow truffle that has become exposed due to soil cracking. This has implication for your management, in terms of encouraging truffles to form at some depth and covering exposed ones.

In one of the other articles in this issue we write about springtails, highlighting the damage they can cause after seeing it in an orchard this season. Property A was the property suffering from springtail damage. If you look back to the charts above you can see that there was almost no damage attributed to slugs and slaters and very few were found using tile and pitfall monitoring. But that’s not to say they had no damage. The chart below breaks down what was causing damage in the exposed, shallow and deep truffles at property A. They had a bit of rot but the vast majority of damage was attributed to springtails.

chart
Every orchard has a different pest and damage profile. The majority of damage to truffles at property A was due to springtails.

This highlights why it is important to monitor for pests while your crop is growing, and also to observe and takes notes during harvest and grading to determine what is present in your orchard and what is causing damage. Every orchard is different.

Grading

It should come as no surprise that with the higher level of damage to exposed truffles more of these truffles was trimmed during grading – see, the chart below where the amount of truffle that required removal due to rot or damage is shown in red. The red portion that goes to trim, peel, industrial grade or trash are much lower value than whole pieces.

chart

As part of our assessment we assigned a grade to each truffle prior to trimming, ignoring the damage by invertebrates. So taking into account shape, size, colour, aroma, what grade would that truffle have been if it hadn’t been chewed on. After trimming each truffle was graded again. This gave us an idea of the amount of downgrading due to invertebrates.

This data was combined with some season average wholesale values for the different grades and is shown in the chart below, with pre trim values on the left and post trim values on the right. The green line is the average for exposed truffles across the six properties for the whole season, the orange line is shallow truffles, and the grey line is deep truffles. The blue dashed line is the average across the season for all properties and depths of truffles. This shows that on average invertebrate damage led to the value dropping from over $900/kg to $825/kg, that is 5% loss just from damage resulting in a lower grade of truffle. On average, there was a bigger drop in potential value of truffles in those that were exposed, reflecting the higher level of damage seen in exposed truffles.

chart

In summary the main messages from the harvest assessments are:

  • Slugs and slaters are widespread and when abundant can cause significant damage.
  • Exposed truffles are more likely to be damaged by invertebrates and rot.
  • Every orchard is different, get to know your pests.
  • Invertebrates are likely chewing into your bottom line.

We would like to take this opportunity to thank the growers that allowed us to undertake harvest assessments with them. We understand that harvest is a very busy time of year and having an extra body or two around can add to an already hectic schedule. Without their help, work like this would not be possible, thank you.